Collimator and energy degrader

ABSTRACT

A particle therapy system includes a particle accelerator to output a particle beam; and a scanning system for the particle accelerator to scan the particle beam across at least part of an irradiation target. The scanning system is configured to scan the particle beam in two dimensions that are at an angle relative to a direction of the particle beam. A structure defines an edge. The structure is controllable to move in the two dimensions relative to the irradiation target such that at least part of the structure is between at least part of the particle beam and the irradiation target. The structure includes a material that inhibits transmission of the particle beam.

TECHNICAL FIELD

This disclosure relates generally to elements of a particle beamscanning system, such as a collimator and an energy degrader.

BACKGROUND

Particle therapy systems use an accelerator to generate a particle beamfor treating afflictions, such as tumors. In operation, particles areaccelerated in orbits inside a cavity in the presence of a magneticfield, and are removed from the cavity through an extraction channel. Amagnetic field regenerator generates a magnetic field bump near theoutside of the cavity to distort the pitch and angle of some orbits sothat they precess towards, and eventually into, the extraction channel.A beam, comprised of the particles, exits the extraction channel.

A scanning system is down-beam of the extraction channel. In thiscontext, “down-beam” means closer to an irradiation target (here,relative to the extraction channel). The scanning system moves the beamacross at least part of the irradiation target to expose various partsof the irradiation target to the beam. For example, to treat a tumor,the particle beam may be “scanned” over different cross-sections of thetumor.

SUMMARY

An example particle therapy system comprises a particle accelerator tooutput a particle beam; and a scanning system for the particleaccelerator to scan the particle beam across at least part of anirradiation target. The scanning system is configured to scan theparticle beam in two dimensions that are at an angle relative to adirection of the particle beam. A structure defines an edge. Thestructure is controllable to move in the two dimensions relative to theirradiation target such that at least part of the structure is betweenat least part of the particle beam and the irradiation target. Thestructure comprises a material that inhibits transmission of theparticle beam. The example particle therapy system may include one ormore of the following features, either alone or in combination.

The structure may be rotatable at least in the two dimensions so thatthe edge can be moved between different parts of the irradiation targetand the particle beam. The edge may comprise a curve that has a radiusthat varies on at least one side of the structure. The curve may be aFrench curve. The structure may define an aperture and the edge maycomprise an edge of the aperture. The structure may be movable to tracka direction of the particle beam. The structure may comprise multipleelements that are adjustable to vary a size of the edge. The multipleelements may comprise fingers that are individually movable relative tothe irradiation target.

The structure may be part of a collimator system. The structure maycomprise a first structure in the collimator system and the edge maycomprise a first edge. The collimator system may comprise a secondstructure comprising a second edge. The first edge and the second edgemay be controllable to move along different edges of the irradiationtarget.

The scanning system may comprise at least one magnet to control movementof the particle beam to scan the particle beam. The at least one magnetmay be for generating a magnetic field in response to applied current.The magnetic field may affect the movement.

The scanning system may be configured to scan the particle beam morequickly in interior sections of the irradiation target than at edges ofthe irradiation target. The particle beam may be movable within an areaof a plane at a location of the structure. The structure may have anarea that is less than the area of the plane. The structure may have anarea that is less than half the area of the plane. The structure mayhave an area that is less than a quarter the area of the plane. Thestructure may have an area that is less than an eighth the area of theplane. The structure may have an area that is less than ten times across-sectional area of the particle beam.

The scanning system may be configured to scan the particle beam fromdifferent incident angles. The structure may be controllable to movebased on movement of the particle beam as the particle beam is scannedfrom different incident angles. The scanning system may comprise: amagnet to affect a direction of the particle beam to scan the particlebeam across at least part of an irradiation target; and a degrader tochange an energy of the beam prior to output of the particle beam to theirradiation target, where the degrader is down-beam of the magnetrelative to the particle accelerator. The particle accelerator may be avariable-energy device.

The particle accelerator may comprise: a voltage source to provide aradio frequency (RF) voltage to a cavity to accelerate particles from aplasma column, where the cavity has a magnetic field causing particlesaccelerated from the plasma column to move orbitally within the cavity;an extraction channel to receive the particles accelerated from theplasma column and to output the received particles from the cavity; anda regenerator to provide a magnetic field bump within the cavity tothereby change successive orbits of the particles accelerated from theplasma column so that, eventually, particles output to the extractionchannel. The magnetic field may be between 4 Tesla (T) and 20 T and themagnetic field bump is at most 2 Tesla.

An example particle therapy system comprises: a particle accelerator tooutput a particle beam; and a scanning system to receive the particlebeam from the particle accelerator and to perform scanning of at leastpart of an irradiation target with the particle beam. The scanningsystem comprises a structure defining an edge. The structure iscontrollable to move in the two dimensions and to move based on movementof the particle beam so that the edge is between at least part of theparticle beam and the irradiation target. The structure comprises amaterial that inhibits transmission of the particle beam. The examplesystem also comprises a gantry on which the particle accelerator and thescanning system are mounted. The gantry may be configured to move theparticle accelerator and the scanning system around the irradiationtarget.

An example particle therapy system comprises: a synchrocyclotron tooutput a particle beam; a magnet to affect a direction of the particlebeam to move the particle beam across a cross-section of an irradiationtarget; a degrader to change an energy of the particle beam prior tomoving the particle beam across the cross-section of the irradiationtarget, where the degrader is down-beam of the magnet relative to thesynchrocyclotron; and one or more processing devices to control movementof the degrader so that the degrader at least partly tracks movement ofthe particle beam at an irradiation plane. The example particle therapysystem may include one or more of the following features, either aloneor in combination.

The particle beam may be movable within an area of a plane at a locationof the degrader. The degrader may have an area that is less than thearea of the plane. The degrader may comprise multiple pieces, with eachpiece comprised of beam-energy absorbing material, and with each piecebeing movable into a path of the particle beam. The one or moreprocessing devices may be programmed to receive an energy of theparticle beam to apply to the irradiation target, and to move one ormore of the pieces of the beam-energy absorbing material into the pathof the particle beam so that a resulting energy of the particle beamapproximates the energy of the particle beam to apply to the irradiationtarget. The one or more processing devices may be programmed to controlmovement of the one or more pieces of the beam-energy absorbing materialto at least partly track movement of the particle beam.

The degrader may have an area that is less than half the area of theplane. The degrader may have an area that is less than one-quarter thearea of the plane. The particle beam has a spot size at a location ofthe degrader; and the degrader may have an area that is less than tentimes an area of the spot size. The degrader may have an area that isless than twice an area of the spot size.

The particle therapy system may comprise memory to store a treatmentplan. The treatment plan may comprise information to define a scanningpattern for the irradiation target. The scanning pattern may definemovement of the particle beam in the two dimensions and movement of thedegrader so that the degrader at least partly tracks movement of theparticle beam.

The synchrocyclotron may comprise: a voltage source to provide a radiofrequency (RF) voltage to a cavity to accelerate particles from a plasmacolumn, where the cavity has a magnetic field causing particlesaccelerated from the plasma column to move orbitally within the cavity;an extraction channel to receive the particles accelerated from theplasma column and to output the received particles from the cavity aspart of the particle beam; and a regenerator to provide a magnetic fieldbump within the cavity to thereby change successive orbits of theparticles accelerated from the plasma column so that, eventually,particles output to the extraction channel. The magnetic field may bebetween 4 Tesla (T) and 20 T and the magnetic field bump may be at most2 Tesla, and the synchrocyclotron may be a variable-energy device.

The magnet and the degrader may be part of a scanning system. Theparticle therapy system may comprise a gantry on which thesynchrocyclotron and the scanning system are mounted. The gantry may beconfigured to move the synchrocyclotron and the scanning system aroundthe irradiation target.

The scanning system may be a raster scanning system, a spot scanningsystem, or any other type of scanning system

An example particle therapy system may comprise a particle acceleratorto output a particle beam; and a scanning system to receive the particlebeam from the synchrocyclotron and to perform scanning of at least partof an irradiation target with the particle beam. The scanning system maycomprise a degrader to change an energy of the particle beam prior toscanning the at least part of the irradiation target. The degrader maybe down-beam of the magnet relative to the synchrocyclotron. The exampleparticle therapy system may comprise one or more processing devices tocontrol movement of the degrader so that the degrader at least partlytracks movement of the particle beam during; and a gantry on which theparticle accelerator and the scanning system are mounted. The gantry maybe configured to move the synchrocyclotron and the scanning systemaround the irradiation target. The example particle therapy system mayinclude one or more of the following features, either alone or incombination.

The particle beam may be movable within an area of a plane at a locationof the degrader. The degrader may have an area that is less than thearea of the plane. The degrader may comprise multiple pieces, with eachpiece comprised of beam-energy absorbing material, and with each piecebeing movable into a path of the particle beam. The one or moreprocessing devices may be programmed to receive an energy of theparticle beam to apply to the irradiation target, and to move one ormore of the pieces of the beam-energy absorbing material into the pathof the particle beam so that a resulting energy of the particle beamapproximates the energy of the particle beam to apply to the irradiationtarget. The one or more processing devices may be programmed to controlmovement of the one or more pieces of the beam-energy absorbing materialto at least partly track movement of the particle beam.

The degrader may have an area that is less than half the area of theplane. The degrader may have an area that is less than one-quarter thearea of the plane. The particle beam has a spot size at a location ofthe degrader, and the degrader may have an area that is less than tentimes an area of the spot size. The degrader may have an area that isless than twice an area of the spot size. The particle accelerator maybe a variable-energy synchrocyclotron.

An example proton therapy system may include the foregoing particleaccelerator and scanning system; and a gantry on which the particleaccelerator and scanning system are mounted. The gantry is rotatablerelative to a patient position. Protons are output essentially directlyfrom the particle accelerator and through the scanning system to theposition of an irradiation target, such as a patient. The particleaccelerator may be a synchrocyclotron.

Two or more of the features described in this disclosure, includingthose described in this summary section, may be combined to formimplementations not specifically described herein.

Control of the various systems described herein, or portions thereof,may be implemented via a computer program product that includesinstructions that are stored on one or more non-transitorymachine-readable storage media, and that are executable on one or moreprocessing devices. The systems described herein, or portions thereof,may be implemented as an apparatus, method, or electronic system thatmay include one or more processing devices and memory to storeexecutable instructions to implement control of the stated functions.

The details of one or more implementations are set forth in theaccompanying drawings and the description below. Other features,objects, and advantages will be apparent from the description anddrawings, and from the claims.

DESCRIPTION OF THE DRAWINGS

FIGS. 1 and 2 are a cross-sectional views of an example synchrocyclotronfor use in a particle therapy system.

FIG. 3 is a side view of an example scanning system.

FIG. 4 is a perspective view of components of an example scanningsystem, excluding scattering material for spot size variation.

FIG. 5 is a front view of an example magnet for use in a scanning systemof the type shown in FIGS. 3 and 4.

FIG. 6 is a perspective view of an example magnet for use in a scanningsystem of the type shown in FIGS. 3 and 4.

FIG. 7 is a perspective view of an example energy degrader (rangemodulator) for use in a scanning system of the type shown in FIGS. 3 and4.

FIG. 8 is a perspective view of a process for moving a plate of anenergy degrader in the path of a particle beam

FIG. 9 is a side view of an example particle beam and collimator.

FIG. 10 is a top view show an example cross-section of an irradiationtarget, an example collimator that is movable along the edge of thecross-section, and an example beam scanning path along an interior ofthe irradiation target.

FIG. 11 is a top view of an example collimator.

FIG. 12 is a top view of components of an example collimator.

FIG. 13 is a top view showing the components of FIG. 12 combined to forman example collimator.

FIG. 14 is a top view show an example cross-section of an irradiationtarget, and an example multi-leaf collimator that is movable along theedge of the cross-section during particle beam scanning.

FIG. 15 is a top view show an example cross-section of an irradiationtarget, and an example straight-edge collimator that is movable androtatable along the edge of the cross-section during particle beamscanning.

FIG. 16 is a top view show an example cross-section of an irradiationtarget, an example multi-part collimator that is movable along the edgesof the cross-section during particle beam scanning, and an example beamscanning paths along an interior of the irradiation target.

FIG. 17 is a top view of an example curved collimator.

FIG. 18 is a view show an example cross-section of an irradiationtarget, and an example of how intensity-modulated proton therapy isperformed on the irradiation target.

FIG. 19 is a perspective view of an example irradiation field of aparticle beam scanning system.

FIG. 20 is a perspective view of multiple pieces of an example energydegrader in the beam path to an irradiation target.

FIG. 21 is a perspective view illustrating movement of pieces of anenergy degrader to track scanning of a particle beam.

FIG. 22 is a perspective view illustrating situations where movement ofpieces of an energy degrader is required, and is not required, to trackscanning of a particle beam.

FIG. 23 is a perspective view of an example therapy system.

FIG. 24 is an exploded perspective view of components of an examplesynchrocyclotron for use in the particle therapy system.

FIG. 25 is a cross-sectional view of the example synchrocyclotron.

FIG. 26 is a perspective view of the example synchrocyclotron.

FIG. 27 is a cross-sectional view of an example ion source for use inthe synchrocyclotron.

FIG. 28 is a perspective view of an example dee plate and an exampledummy dee for use in the synchrocyclotron.

FIG. 29 shows a patient positioned within an example inner gantry of theexample particle therapy system in a treatment room.

FIG. 30 is a conceptual view of an example particle therapy system thatmay use a variable-energy particle accelerator.

FIG. 31 is an example graph showing energy and current for variations inmagnetic field and distance in a particle accelerator.

FIG. 32 is a side view of an example structure for sweeping voltage on adee plate over a frequency range for each energy level of a particlebeam, and for varying the frequency range when the particle beam energyis varied.

FIG. 33 is a perspective, exploded view of an example magnet system thatmay be used in a variable-energy particle accelerator.

Like reference symbols in the various drawings indicate like elements.

DETAILED DESCRIPTION

Described herein is an example of a particle accelerator for use in asystem, such as a proton or ion therapy system. The example particletherapy system includes a particle accelerator—in this example, asynchrocyclotron—mounted on a gantry. The gantry enables the acceleratorto be rotated around a patient position, as explained in more detailbelow. In some implementations, the gantry is steel and has two legsmounted for rotation on two respective bearings that lie on oppositesides of a patient. The particle accelerator is supported by a steeltruss that is long enough to span a treatment area in which the patientlies and that is attached at both ends to the rotating legs of thegantry. As a result of rotation of the gantry around the patient, theparticle accelerator also rotates.

In an example implementation, the particle accelerator (e.g., thesynchrocyclotron) includes a cryostat that holds one or moresuperconducting coils, each for conducting a current that generates amagnetic field (B). In this example, the cryostat uses liquid helium(He) to maintain each coil at superconducting temperatures, e.g., 4°Kelvin (K). Magnetic yokes or smaller magnetic pole pieces are locatedinside the cryostat, and define a cavity in which particles areaccelerated.

In this example implementation, the particle accelerator includes aparticle source (e.g., a Penning Ion Gauge—PIG source) to provide aplasma column to the cavity. Hydrogen gas is ionized to produce theplasma column. A voltage source provides a radio frequency (RF) voltageto the cavity to accelerate pulses of particles from the plasma column.

As noted, in an example, the particle accelerator is a synchrocyclotron.Accordingly, the RF voltage is swept across a range of frequencies toaccount for relativistic effects on the particles (e.g., increasingparticle mass) when accelerating particles from the plasma column. Themagnetic field produced by running current through a superconductingcoil causes particles accelerated from the plasma column to accelerateorbitally within the cavity. In other implementations, a particleaccelerator other than a synchrocyclotron may be used. For example, acyclotron, a synchrotron, a linear accelerator, and so forth may besubstituted for the synchrocyclotron described herein.

In the synchrocyclotron, a magnetic field regenerator (“regenerator”) ispositioned near the outside of the cavity (e.g., at an interior edgethereof) to adjust the existing magnetic field inside the cavity tothereby change locations (e.g., the pitch and angle) of successiveorbits of the particles accelerated from the plasma column so that,eventually, the particles output to an extraction channel that passesthrough the cryostat. The regenerator may increase the magnetic field ata point in the cavity (e.g., it may produce a magnetic field “bump” atan area of the cavity), thereby causing each successive orbit ofparticles at that point to precess outwardly toward the entry point ofthe extraction channel until it reaches the extraction channel. Theextraction channel receives particles accelerated from the plasma columnand outputs the received particles from the cavity as a particle beam.

The superconducting (“main”) coils can produce relatively high magneticfields. The magnetic field generated by a main coil may be within arange of 4 T to 20 T or more. For example, a main coil may be used togenerate magnetic fields at, or that exceed, one or more of thefollowing magnitudes: 4.0 T, 4.1 T, 4.2 T, 4.3 T, 4.4 T, 4.5 T, 4.6 T,4.7 T, 4.8 T, 4.9 T, 5.0 T, 5.1 T, 5.2 T, 5.3 T, 5.4 T, 5.5 T, 5.6 T,5.7 T, 5.8 T, 5.9 T, 6.0 T, 6.1 T, 6.2 T, 6.3 T, 6.4 T, 6.5 T, 6.6 T,6.7 T, 6.8 T, 6.9 T, 7.0 T, 7.1 T, 7.2 T, 7.3 T, 7.4 T, 7.5 T, 7.6 T,7.7 T, 7.8 T, 7.9 T, 8.0 T, 8.1 T, 8.2 T, 8.3 T, 8.4 T, 8.5 T, 8.6 T,8.7 T, 8.8 T, 8.9 T, 9.0 T, 9.1 T, 9.2 T, 9.3 T, 9.4 T, 9.5 T, 9.6 T,9.7 T, 9.8 T, 9.9 T, 10.0 T, 10.1 T, 10.2 T, 10.3 T, 10.4 T, 10.5 T,10.6 T, 10.7 T, 10.8 T, 10.9 T, 11.0 T, 11.1 T, 11.2 T, 11.3 T, 11.4 T,11.5 T, 11.6 T, 11.7 T, 11.8 T, 11.9 T, 12.0 T, 12.1 T, 12.2 T, 12.3 T,12.4 T, 12.5 T, 12.6 T, 12.7 T, 12.8 T, 12.9 T, 13.0 T, 13.1 T, 13.2 T,13.3 T, 13.4 T, 13.5 T, 13.6 T, 13.7 T, 13.8 T, 13.9 T, 14.0 T, 14.1 T,14.2 T, 14.3 T, 14.4 T, 14.5 T, 14.6 T, 14.7 T, 14.8 T, 14.9 T, 15.0 T,15.1 T, 15.2 T, 15.3 T, 15.4 T, 15.5 T, 15.6 T, 15.7 T, 15.8 T, 15.9 T,16.0 T, 16.1 T, 16.2 T, 16.3 T, 16.4 T, 16.5 T, 16.6 T, 16.7 T, 16.8 T,16.9 T, 17.0 T, 17.1 T, 17.2 T, 17.3 T, 17.4 T, 17.5 T, 17.6 T, 17.7 T,17.8 T, 17.9 T, 18.0 T, 18.1 T, 18.2 T, 18.3 T, 18.4 T, 18.5 T, 18.6 T,18.7 T, 18.8 T, 18.9 T, 19.0 T, 19.1 T, 19.2 T, 19.3 T, 19.4 T, 19.5 T,19.6 T, 19.7 T, 19.8 T, 19.9 T, 20.0 T, 20.1 T, 20.2 T, 20.3 T, 20.4 T,20.5 T, 20.6 T, 20.7 T, 20.8 T, 20.9 T, or more. Furthermore, a maincoil may be used to generate magnetic fields that are within the rangeof 4 T to 20 T (or more, or less) that are not specifically listedabove.

In some implementations, such as the implementation shown in FIGS. 1 and2, large ferromagnetic magnetic yokes act as a return for stray magneticfield produced by the superconducting coils. For example, in someimplementations, the superconducting magnet can generate a relativelyhigh magnetic field of, e.g., 4 T or more, resulting in considerablestray magnetic fields. In some systems, such as that shown in FIGS. 1and 2, the relatively large ferromagnetic return yoke 100 are used as areturn for the magnetic field generated by superconducting coils. Amagnetic shield surrounds the yoke. The return yoke and the shieldtogether dissipated stray magnetic field, thereby reducing thepossibility that stray magnetic fields will adversely affect theoperation of the accelerator.

In some implementations, the return yoke and shield may be replaced by,or augmented by, an active return system. An example active returnsystem includes one or more active return coils that conduct current ina direction opposite to current through the main superconducting coils.In some example implementations, there is an active return coil for eachsuperconducting coil, e.g., two active return coils—one for eachsuperconducting coil (referred to as a “main” coil). Each active returncoil may also be a superconducting coil that surrounds the outside of acorresponding main superconducting coil.

Current passes through the active return coils in a direction that isopposite to the direction of current passing through the main coils. Thecurrent passing through the active return coils thus generates amagnetic field that is opposite in polarity to the magnetic fieldgenerated by the main coils. As a result, the magnetic field generatedby an active return coil is able to dissipate at least some of therelatively strong stray magnetic field resulting from the correspondingmain coil. In some implementations, each active return may be used togenerate a magnetic field of between 2.5 T and 12 T or more. An exampleof an active return system that may be used is described in U.S. patentapplication Ser. No. 13/907,601, filed on May 31, 2013, the contents ofwhich are incorporated herein by reference.

Referring to FIG. 3, at the output of extraction channel 102 of particleaccelerator 105 (which may have the configuration shown in FIGS. 1 and2), is an example scanning system 106 that may be used to scan theparticle beam across at least part of an irradiation target. FIG. 4shows examples of components of the scanning system. These include, butare not limited to, a scanning magnet 108, an ion chamber 109, and anenergy degrader 110. Other components that may be incorporated into thescanning system are not shown in FIG. 4, including, e.g., one or morescatterers for changing beam spot size.

In an example operation, scanning magnet 108 is controllable in twodimensions (e.g., Cartesian XY dimensions) to direct the particle beamacross a part (e.g., a cross-section) of an irradiation target. Ionchamber 109 detects the dosage of the beam and feeds-back thatinformation to a control system to adjust beam movement. Energy degrader110 is controllable to move material into, and out of, the path of theparticle beam to change the energy of the particle beam and thereforethe depth to which the particle beam will penetrate the irradiationtarget.

FIGS. 5 and 6 shows views of an example scanning magnet 108. Scanningmagnet 108 includes two coils 111, which control particle beam movementin the X direction, and two coils 112, which control particle beammovement in the Y direction. Control is achieved, in someimplementations, by varying current through one or both sets of coils tothereby vary the magnetic field(s) produced thereby. By varying themagnetic field(s) appropriately, the particle beam can be moved in the Xand/or Y direction across the irradiation target. In someimplementations, the scanning magnet is not movable physically relativeto the particle accelerator. In other implementations, the scanningmagnet may be movable relative to the accelerator (e.g., in addition tothe movement provided by the gantry). In some implementations, thescanning magnets may be controllable to move the particle beamcontinuously. In other implementations, the scanning magnets arecontrollable at intervals or specific times. In some implementations,there may be different scanning magnets to control movement of the beamin the X and/or Y directions. In some implementations, there may bedifferent scanning magnets to control partial movement of the beam ineither the X and/or Y direction.

In some implementations, ion chamber 109 detects dosage applied by theparticle beam by detecting the numbers of ion pairs created within a gascaused by incident radiation. The numbers of ion pairs correspond to thedosage provided by the particle beam. That information is fed-back to acomputer system that controls operation of the particle therapy system.The computer system (not shown), which may include memory and one ormore processing devices, determines if the dosage detected by ionchamber is the intended dose. If the dosage is not as intended, thecomputer system may control the accelerator to interrupt productionand/or output of the particle beam, and/or control the scanning magnetto prevent output of the particle beam to the irradiation target. Forexample, to prevent or modify output of the particle beam, the computersystem may turn the ion source off/on, change the frequency of the RFsweep, activate one or more mechanisms (such as a fast kicker magnet(not shown)) to divert the beam to an absorber material and therebyprevent the beam output, and so forth.

FIG. 7 shows a range modulator 115, which is an example implementationof energy degrader 110. In some implementations, such as that shown inFIG. 7, range modulator includes a series of plates 116. The plates maybe made of one or more of the following example materials: carbon,beryllium or other material of low atomic number. Other materials,however, may be used in place of, or in addition to, these examplematerials.

One or more of the plates is movable into, or out of, the beam path tothereby affect the energy of the particle beam and, thus, the depth ofpenetration of the particle beam within the irradiation target. Forexample, the more plates that are moved into the path of the particlebeam, the more energy that will be absorbed by the plates, and the lessenergy the particle beam will have. Conversely, the fewer plates thatare moved into the path of the particle beam, the less energy that willbe absorbed by the plates, and the more energy the particle beam willhave. Higher energy particle beams penetrate deeper into the irradiationtarget than do lower energy particle beams. In this context, “higher”and “lower” are meant as relative terms, and do not have any specificnumeric connotations.

Plates are moved physically into, and out of, the path of the particlebeam. For example, as shown in FIG. 8, a plate 116 a moves along thedirection of arrow 117 between positions in the path of the particlebeam and outside the path of the particle beam. The plates arecomputer-controlled. Generally, the number of plates that are moved intothe path of the particle beam corresponds to the depth at which scanningof an irradiation target is to take place. For example, the irradiationtarget can be divided into cross-sections, each of which corresponds toan irradiation depth. One or more plates of the range modulator can bemoved into, or out of, the beam path to the irradiation target in orderto achieve the appropriate energy to irradiate each of thesecross-sections of the irradiation target. Traditionally, the rangemodulator was stationary relative to the particle beam during scanningof a part of (e.g., cross-section of) an irradiation target, except forits plates moving in and out of the path of the particle beam.

In some implementations, the range modulator of FIGS. 7 and 8 may bereplaced with a range modulator that, at least some of the time, tracksmovement of the particle beam. This type of energy degrader is describedin more detail below.

In some implementations, the particle accelerator may be avariable-energy particle accelerator, such as the example particleaccelerator described in U.S. patent application Ser. No. 13/916,401,filed on Jun. 12, 2013, the contents of which are incorporated herein byreference. In example systems where a variable-energy particleaccelerator is used, there may be less need for an energy degrader ofthe type described herein, as the energy level of the particle beam maybe controlled by the particle accelerator. For example, in some systemsthat employ a variable-energy particle accelerator, an energy degradermay not be needed. In some systems that employ a variable-energyparticle accelerator, an energy degrader may still be used to changebeam energy levels.

In some implementations, a treatment plan is established prior totreating the irradiation target. The treatment plan may specify howscanning is to be performed for a particular irradiation target. In someimplementations, the treatment plan specifies the following information:a type of scanning (e.g., spot scanning or raster scanning); scanlocations (e.g., locations of spots to be scanned); magnet current perscan location; dosage-per-spot, spot size; locations (e.g., depths) ofirradiation target cross-sections; particle beam energy percross-section; plates or other types of pieces to move into the beampath for each particle beam energy; and so forth. Generally, spotscanning involves applying irradiation at discrete spots on anirradiation target and raster scanning involves moving a radiation spotacross the radiation target. The concept of spot size therefore appliesfor both raster and spot scanning.

In some implementations, the overall treatment plan of an irradiationtarget includes different treatment plans for different cross-sectionsof the irradiation target. The treatment plans for differentcross-sections may contain the same information or differentinformation, such as that provided above.

In some implementations, the scanning system may include a collimator120 (FIG. 3) to collimate the particle bean, which may include anaperture that is placeable relative to the irradiation target to limitthe extent of the particle beam and thereby alter the shape of the spotapplied to the irradiation target. For example, the collimator may beplaced in the beam path down-beam of the energy degrader and before theparticle beam hits the irradiation target. The collimator may contain anarea (e.g., a hole or a transmissive material) through which theparticle beam passes and another material (e.g., brass) around the holethat inhibits or prevents passage of the particle beam.

In some implementations, the collimator may include a structure definingan edge. The structure may include a material, such as brass, thatinhibits transmission of the particle beam. The structure may becontrollable to move in two dimensions relative to the irradiationtarget so that at least part of the structure is between at least partof the particle beam and the irradiation target. For example, thestructure may be movable in the X and Y directions of a plane thatintersects the particle beam and that is parallel, or substantiallyparallel to, a cross-section of the irradiation target that is beingtreated. Use of a collimator in this manner may be beneficial in that itcan be used to customize the cross-sectional shape of the particle beamthat reaches the patient, thereby limiting the amount of particle beamthat extends beyond the radiation target. For example, as shown in FIG.9, a structure 220 in a collimator prevents portion 221 of particle beam222 from reaching a target 224, thereby limiting the beam to theirradiation target and reducing exposure of healthy tissue 225 toradiation. By placing a structure with an edge between part of theparticle beam and the patient, the example collimator also provides adefined, or sharp, edge to the particle beam portion that reaches thepatient, thereby promoting more precise dose applications.

Positioning and movement of the collimator may be controlled by acontrol computer system that controls other features of the particletherapy system described herein. For example, the collimator may becontrolled in accordance with the treatment plan to track (e.g., follow)motion of the particle beam across at least part of the irradiationtarget. In some implementations, the collimator track is controlled totrack all motion of the particle beam relative to the irradiationtarget. For example, in some implementations, the collimator may becontrolled to track motion of the particle beam throughout the entiretyof the irradiation target, e.g., both at edges of the irradiation targetand at interiors of the irradiation target. In some implementations, thecollimator is controlled to track only some motion of the particle beamrelative to the irradiation target. For example, the collimator may becontrolled to track movement of the particle beam only along the edgesof the irradiation target relative to when the particle beam reachesthose edges.

Referring to FIG. 10, for instance, a particle beam may follow a path inan irradiation target 229 shown by arrowed lines 230. Collimator 231 maynot track motion of the particle beam on the interior 233 of irradiationtarget 229. But, collimator 231 may track motion of the particle beamalong only the edges of the irradiation target (e.g., roughly alongarrow 232). For example, each time the particle beam reaches an edge 234of the irradiation target, the collimator may move, or may havepreviously moved, to intercept the particle beam at the edge, andthereby limit exposure of surrounding tissue 235 to the beam. When, andby how much, the collimator moves may depend on the size of the particlebeam cross-section (spot) and the speed at which the particle beamscans. In this example, there is no need to limit exposure to theparticle beam at the interior of the irradiation target; hence, thecollimator need not track the beam at the interior.

The movement of a collimator may be controlled in various ways. Forexample, the current through magnet 108 may correspond to the deflectionof the particle beam by the magnet and, thus, the location of theparticle beam spot on the irradiation target. So, for example, knowingthe current through the magnet and the location of the irradiationtarget relative to the magnet, a computer system controlling operationof the scanning system can determine the projected location of theirradiation spot. And, knowing the location of the radiation spot, thecomputer system can control the scanning system, in particular thecollimator, to track movement of the irradiation spot along all or partof its motion, as described herein. In some implementations, thecomputer system can control the scanning system, in particular thecollimator, so that the collimator arrives at a location before theparticle beam spot arrives at that location, as described in more detailbelow.

Use of a collimator, such as is described above, can have advantages.For example, in some cases, goals of particle beam scanning may includeachieving accuracy at the edges of an irradiation target and uniformityof dosage or coverage in the interior of the irradiation target. The useof a collimator can help to further these goals by enabling use of arelatively large particle beam spot for scanning. In this context, aspot size may be considered “large” if it has an area that is within aspecified percentage of the area of the irradiation target. Thispercentage might typically be 2.5%, but values between, e.g., 0.25% and25%, could also be used. Scanning using a relative large spot sizeincreases the fractional areal coverage of the irradiation target foreach beam pulse. Typically, the larger the size of this spot, the lessadversely affected the target uniformity will be due to target (patient)motion. At the edges, however, the collimator reduces the chances thatradiation from the large spot will impact tissue (e.g., healthy tissue)outside the radiation target by reducing the lateral penumbra.Traditionally, smaller spot sizes were preferred, since they enabledmore precise dosage at the edges as compared to a larger spot size. But,compared to a collimated edge, those smaller spot sizes could result inslower treatment times for a given treatment volume, and reduced edgeconformality due to reduced edge resolution and increased penumbra.

The collimator may have any number of different shapes or configurationsand may, or may not, include one or more moving parts. In an exampleimplementation, the collimator is comprised of brass and/or otherradiation-blocking material, and has a thickness on the order of severalcentimeters. However, different collimators may have differentcompositions and thicknesses.

In example implementation, the collimator is a structure that has one ormore defined edges. For example, the collimator may be a structurecontaining an aperture, or hole. FIG. 11 shows an example of this typeof collimator 239. Collimator 239 may have any appropriate shape, withan aperture therein. The edges of the aperture may be used to limitapplication of the particle beam, as shown in FIG. 9 for example,thereby allowing application of beam 222 to the irradiation target 224but not to tissue covered by collimator 220 that is otherwise in thebeam path. As explained above, the aperture may track (e.g., follow) theparticle beam throughout all or part of the scanning operation. Forexample, the aperture may track movement of the particle beam only atedges of the irradiation target or throughout the entire motion of thebeam. That is, the collimator itself may move along the edge of theirradiation target to track movement of the particle beam (e.g., so thatthe location of the collimator coincides with the particle beam when theparticle beam reaches the irradiation target edge).

In some implementations, the collimator may include two or moreapertures that are controlled to overlap and thereby achieve a specificsize. For example, as shown in FIG. 12, apertures 244 and 245 are partof respective structures 246 and 247. The structures move relative toeach other, as shown in FIG. 13, thereby causing the apertures 244, 245to overlap and change the size and, in some cases, the shape ofresulting hole 248 through which the particle beam is allowed to pass.Shapes other than those shown may be used.

In some implementations, the collimator may track the movement of theparticle beam during the particle beam's motion in the interior of theirradiation target. For example, in some implementations, the aperturemay have a diameter that is less than the diameter of the particle beamspot. In some systems, it may be desirable to use a spot having aspecific diameter at all irradiation positions (including those on theinterior of the irradiation target). In these systems, therefore, theaperture may track all movement of the particle beam spot so as toachieve the appropriate particle beam spot diameter for treatment. Insome implementations, the aperture of the collimator may vary in sizeand/or shape. For example, the collimator may have one or more movingparts to vary the size and shape of the aperture (e.g., to reduce itsdiameter, surface area, or the like).

In example implementations, the collimator may be a structure having oneor more straight edges. For example, the collimator may include square,rectangular, or substantially linear structures, each having at leastone edge that can be placed in the path of the particle beam.

In an example implementation that employs straight edges, the collimatormay have a multi-leaf structure, as in FIG. 14. In FIG. 14, collimator250 tracks movement along the edge of irradiation target 251. Fingers252 move up or down, or towards or away from the irradiation target, inorder to achieve an edge shape 253 that substantially matches the edgeshape of the irradiation target and that blocks the particle beam fromreaching healthy tissue (or tissue that should not be irradiated). Forexample, each finger can be moved up or down, or extended and retracted,or a combination of such movements to substantially match the edgeshape. Collimator 250 itself may move along the edge of the irradiationtarget 251 (e.g., roughly in the direction of arrow 255) to trackmovement of the particle beam (e.g., so that the location of thecollimator coincides with the particle beam when the particle beamreaches the irradiation target edge). In some implementations,collimator 250 may, or may not, move into the interior of theirradiation target during scanning operations.

Traditional multi-leaf collimators are stationary relative to theirradiation target and include two sets of fingers that face each otherand that move relative to each other to attain the appropriatecollimation. There may be tens, hundreds, or even thousands of fingersused in such collimators, and their size may be as large as theirradiation field itself. In some implementations, the irradiation fieldmay be defined by a plane, which is at an angle to the beam, and whichdefines the maximum extent that a particle beam can move in the X and Ydirections relative to the irradiation target. However, in the exampleimplementations described herein, the collimator moves relative to(e.g., tracks or moves along the edge of) the irradiation target, andneed only provide a defined edge at the point of the irradiation targetwhere and when the spot hits that point. Accordingly, the multi-leafcollimator (in addition to being only a single set of fingers) may bemade considerably smaller than its conventional counterparts. Forexample, the multi-leaf collimators described herein may include ten orless (e.g., two, three, four, five, six, seven, eight or nine) fingers(or more, if desired).

In an example implementation that employs straight edges, as shown inFIG. 15, collimator 260 may be rectangular in shape, and move along theedge of irradiation target 261. Collimator 260 may move along the edgeof the irradiation target to track movement of the particle beam (e.g.,so that the location of the collimator coincides with the particle beamwhen the particle beam reaches the irradiation target edge). Duringmotion along the edge of the irradiation target, collimator 260 may alsorotate in two or three dimensions, e.g., in the XY dimensions of arrow262 and also in the Z dimension. This rotation allows at least a portionof an edge of collimator 260 to match the edge of the irradiation targetrelative closely. Thus, collimator 260 may be appropriately positionedso that, when the particle beam reaches the edge of the irradiationtarget, the collimator blocks the tissue extending beyond the edge. As aresult, the collimator provides a defined radiation edge relative to theirradiation target and protects adjacent tissue from the particle beam.Movement of the collimator to the appropriate point on the edge of theirradiation target may coincide with movement of the particle beam orprecede movement of the particle beam.

In some implementations, the collimator may include a single structurewith one or more straight edges, as shown in FIG. 15. In otherimplementations, the collimator may include two or more such structuresat different (e.g., opposing) edges of the irradiation target, as shownin FIG. 16. There, the collimator includes two structures 265, 266. Eachof structures 265 and 266 tracks movement of the particle beam. That is,structure 265 moves so that the location of structure 265 coincides withthe particle beam when the particle beam reaches edge 269 of theirradiation target, and structure 266 moves so that the location ofstructure 266 coincides with the particle beam when the particle beamreaches edge 270 of the irradiation target. Movement of each structureto the appropriate point on the edge of the irradiation target maycoincide with movement of the particle beam or precede movement of theparticle beam. For example, structure 266 can be moved as the spot isscanned in the direction of arrow 271, so that structure 266 is in theappropriate location when the spot returns to edge 270; and structure265 can be moved as the spot is scanned in the direction of arrow 272,so that structure 265 is in the appropriate location when the spotreturns to edge 269. Structures 265 and 266 may move at the same times,at different times, or there may be overlap in the times of theirmovement. An arrangement of this type enables the particle beam to bemoved from edge to edge of the irradiation target, with the collimatorenabling a defined irradiation field at both edges. And, since thecollimator is comprised of multiple structures, scanning need not besignificantly slowed waiting for movement of the collimator. In someimplementations, the collimator may include more than two (e.g., three,four, etc.) structures of the type and operation shown in FIG. 16. Insome implementations, the two or more structures that make up thecollimator may be structures that include holes, such as that shown inFIG. 11. The operation of the two-structure collimator is otherwise asdescribed above.

In some implementations, the collimator need not have a straight edge,but rather its edge(s) may be curved, as shown in FIG. 17. A collimatormay include only one such structure or two or more such structures. Insome implementations, the two or more structures that make up thecollimator may be structures that include curved edges. For example, twostructures of the type shown in FIG. 17 may replace the two structuresof FIG. 16. The operation of the two-structure collimator is otherwiseas described above.

In this regard, in example implementations, the collimator may be astructure having a curved shape having a radius of curvature that variescontinuously along its edge, thereby enabling at least part of the edgeto closely match the edge of an irradiation target, either directly orby rotating the edge at an appropriate angle. In this example,collimator 275 is a French curve that can be moved to track the beam,either partly or fully, and that can be rotated in two or threedimensions relative to the irradiation target to control application ofthe particle beam. Any appropriately curved structure may be include inthe collimator. As was the case above, collimator 275 may only movealong the edge of the irradiation target to track movement of theparticle beam (e.g., so that the location of the collimator coincideswith the particle beam when the particle beam reaches the irradiationtarget edge). As was the case above, the collimator may, or may not,track movement of the particle beam at the interior of the irradiationtarget.

A collimator may include only one structure of the type shown in FIG. 17or the collimator may include two or more such structures. For example,two structures of the type shown in FIG. 17 may replace the twostructures of FIG. 16. The operation of the two-structure collimator isotherwise as described above.

In some implementations, the treatment planning system may be designedso that the scanning speed (e.g., the rate at which the particle beamspot traverses the irradiation target) is different in the interior ofthe irradiation target than at the edges of the irradiation target. Forexample, the scanning speed may be faster at the interior of theirradiation target than at the edges of the irradiation target. Thisarrangement allows for higher precision scanning at the edges of theirradiation target than at the interior of the irradiation target. Thistype of variable-speed scanning may be implemented using any appropriatetype of collimator, including those described herein, or this type ofvariable-speed scanning may be implemented without using any collimator.In either case, the slower speed at the irradiation target edge mayenable more precise scanning there, which may reduce the chances thatthe particle beam will impact outside the irradiation target.

In some implementations, the collimator described herein may be used inan intensity-modulated proton therapy process. In such as process, theproton beam is projected at the radiation target from differentdirections so that a percentage of the overall dose is delivered fromeach direction. As a result, the amount of dose delivered to volumesoutside of the irradiation target can be reduced. For example, FIG. 18shows a particle beam 280 applied to the irradiation target 281 fromthree different angles. In this example, ⅓ of the total dose may beapplied from one angle; ⅓ of the total dose may be applied from anotherangle; and ⅓ of the total dose may be applied from yet another angle.That is, the particle beam may be scanned at angle 282 relative tohorizontal 285 to apply ⅓ of the dose; the particle beam may be scannedat angle 283 to apply ⅓ of the dose; and the particle beam may bescanned at angle 284 to apply ⅓ of the dose. As a result, the amount ofradiation applied to surrounding tissue 287 is spread out at theappropriate angles, thereby reducing the chances that surrounding tissuewill be exposed to harmful amounts of radiation. Any appropriate numberof angles and appropriate dosage per angle may be employed.

Irradiation targets, such as tumors, typically are not symmetric.Accordingly, different beam collimation is typically required for thedifferent angles of application of the particle beam. The examplecollimators described herein can be positioned at the appropriatelocations along the irradiation target's edge (as described above) toprovide appropriate collimation given the angle of irradiation. In someimplementations, the example collimators can track motion of theparticle beam, either only at the irradiation target's edge orthroughout some portion (e.g., all) of the motion of the particle beamat all angles of application.

In some implementations, the example collimators described hereinprevent transmission of the particle beam to surrounding tissue byblocking the particle beam. In some implementations, the examplecollimators may enable partial transmission of the particle beam,thereby resulting in application of lower-levels of radiation to thesurrounding tissue than to the irradiation target. Any of the examplecollimators described herein may be produced in this manner.

The example collimators described herein may be mounted to one or morecomputer-controlled robotic arms or other structures to control theirmovement relative to the irradiation target. A collimator may be mountedto the scanning system itself as well. Typically, the collimator ismounted closest to the patent relative to other elements of the particlebeam scanning system (e.g., down-beam of other elements of the scanningsystem). In implementations where the collimator includes more than onepiece (e.g., FIG. 16), there may be more than one robotic arm or otherstructure to independently control the different pieces of thecollimator in accordance with the treatment plan. In someimplementations, a single robotic arm may be configured to control thedifferent pieces of the collimator independently or to control acombination of pre-assembled pieces.

In some implementations, the energy degrader may also configured totrack motion of the particle beam. In this regard, in someimplementations, such as the example implementation described withrespect to FIGS. 7 and 8, the energy degrader may include multipleplates that are movable into the path of the particle beam to controlthe amount of energy in the beam and thereby control the depth to whichthe particle beam penetrates the irradiation target. In this way, theenergy degrader is used to perform depth (the direction of the particlebeam or Z-direction) scanning in the irradiation target. Typically, eachplate absorbs an amount of energy in the particle beam. Accordingly, themore plates that are placed in front of the particle beam, the lessenergy the beam has, and the less deep the beam will penetrate into theirradiation target. Conversely, the fewer plates that are placed infront of the particle beam, the more energy the beam has (since lessenergy is absorbed by the plate(s)), and the more deep the beam willpenetrate into the irradiation target. In some implementations, eachplate has about the same thickness, and therefore absorbs about the sameamount of beam energy. In other implementations, different plates mayhave different thicknesses, with the thickness of a plate correspondingto the amount of energy that the plate absorbs.

In some implementations, the plates each have a surface area that isabout the size of the irradiation field. In this context, theirradiation field may be defined by a plane that defines the maximumextent that a particle beam can move in the X and Y directions relativeto the irradiation target. For example, FIG. 19 shows an irradiationfield 290 in front of an irradiation target 291. Due to physical systemlimitations, a particle beam is movable across, but not beyond, theplane defining the irradiation field. Accordingly, to ensure that theenergy degrader can be applied to any location within the irradiationfield, in some implementations the plates in the energy degrader eachhave a surface are that is at least as big as, and in some cases thatexceeds, the size of the irradiation field. This configuration, however,can result in plates that are large (e.g., possibly a square meter orsquare meters), and thus that can be heavy and relative slow to move.Slow movement of the plates can result in slower treatment.

In some implementations, the energy degraders may be smaller than thesize of the irradiation field, and track at least part of the motion ofthe particle beam. As a result, the energy degrader may be lighter,which can reduce the amount of time that it takes to position the energydegrader plates in the path of the particle beam and thus reduce thetreatment time. The energy degrader may track the particle beam in twodirections (e.g., XY) or in three directions (e.g., XYZ). That is, theenergy degrader may move in a plane perpendicular to the particle beam,or the energy degrader may move in a plane perpendicular to the particlebeam and along a longitudinal direction of the particle beam. In thisregard, any of the collimators described herein may also move in a planeperpendicular to the particle beam, or any of the collimators describedherein may also move in a plane perpendicular to the particle beam andalong a longitudinal direction of the particle beam. Movement of thecollimator(s) and energy degrader(s) may be independent or coordinated.

For example, an energy degrader may be comprised of multiple pieces,which may be plates or other structures constructed to absorb particlebeam energy during treatment. Each piece may have the same area (XY) andthickness (Z) or different pieces may have different areas andthicknesses. Referring to FIG. 20, two or more pieces 294 having thesame or different thicknesses may be placed in front an irradiationtarget 295 in the particle beam 293 path to achieve a particular amountof energy absorption. Alternatively, a single piece having a specifiedthickness may be placed in front of the beam to achieve a particularamount of energy absorption. For example, if a particular energyabsorption is needed, the control computer may select a piece with theappropriate thickness to achieve that absorption.

In examples where two or more pieces are placed in front of the beam,those pieces may be assembled prior to placement or assembleddynamically during placement. For example, the control computer mayselect two pieces, arrange them, and then move the combination of thetwo pieces into the beam path. Alternatively, the control computer mayselect two pieces and then move the combination of the two pieces intothe beam path simultaneously but not in combination (e.g., each may bemoved with a separate robotic arm).

The energy degrader, or pieces thereof, may track movement of theparticle beam across at least part of the irradiation field so as toachieve appropriate energy absorption, and thus beam depth penetration,at various points on the irradiation target. The treatment plan maydictate where the energy degrader needs to be at any particular timeduring treatment, and feedback from the ionization chamber may be usedfor positioning and position correction, if necessary. In someimplementations, the precision with which the energy degrader needs totrack the particle beam is based on the size of the degrader and thespot size of the particle beam at the point where the particle beamintersects the energy degrader.

More specifically, in some examples, the smaller that the surface areaof the energy degrader is, the more closely movement of the energydegrader should track movement of the particle beam. Conversely, inother examples, the larger that the surface area of the energy degraderis, the less closely movement of the energy degrader needs to trackmovement of the particle beam. For example referring to FIG. 21, if theenergy degrader 299 has a surface area that is close to a surface areaof spot 300 at the point where the particle beam intersects the energydegrader, the energy degrader should track motion of the particle beamrather closely in order to ensure that the energy degrader is in frontof the particle beam relative to irradiation target 301 at appropriatetimes during treatment. For example, motion of particle beam 304 fromlocation 302 to location 303 would also require energy degrader 299 tomove in the direction of arrow 305 to remain in the beam path, since theareas of the spot and the degrader are relatively close in size. Asindicated, motion of the particle beam may be dictated by the treatmentplan and detected through use of the ionization chamber and feedback tothe control computer. This information may also be used to controlmovement of the energy degrader.

In some implementations, the moveable energy degrader may beconsiderably larger than the particle beam spot. In these cases, theenergy degrader need not track motion of the particle beam as closely inorder to ensure that the energy degrader is in front of the particlebeam at appropriate times during treatment. In fact, depending upon thesize of the energy degrader, the energy degrader need not move at all insome cases where the particle beam moves. That is, for some motion ofthe particle beam, the energy degrader may remain stationary, but forother motion of the particle beam, the energy degrader also moves tointercept the particle beam. For example, FIG. 22 shows a case where theenergy degrader 310 is considerably larger than particle beam spot 311at the point where the particle beam intersects the energy degrader. Asthe particle beam spot moves from point 314 a to point 314 b, the energydegrader remains in the beam path even though the energy degrader hasnot moved. The control computer system, knowing the size of the degraderand the two spot positions, does not move the energy degrader in thiscase. Accordingly, in this case, the energy degrader need not trackmovement of the particle beam spot. However, when the spot moves topoint 314 c, the energy degrader (or piece(s) thereof) will move totrack and intercept the beam so as to remain in the beam path.Accordingly, the size of the energy degrader relative to the beam spotis a factor in determining when, and by how much, the energy degrader isrequired to move during scanning.

In some implementations, the energy degrader may include multiple partsor pieces. For example, one part or piece may be used to track movementof the particle beam across part of an irradiation target (e.g.,irradiation applied from the top of the irradiation target) and anotherpart or piece may be used to track movement of the particle beam acrossanother part of an irradiation target (e.g., irradiation applied fromthe bottom of the target).

The energy degrader (or pieces thereof) may have any shape, e.g.,square, rectangular, circular, oval, irregular, regular, polygonal,spherical, cubical, tetrahedral, and so forth. The energy degrader (orpieces thereof) may have any appropriate size. For example, the energydegrader (or pieces thereof) may have a surface area this less than thearea of the irradiation field, that is less than ¾ the area of theirradiation field, that is less than ½ the area of the irradiationfield, that is less than ⅓ the area of the irradiation field, that isless than ¼ the area of the irradiation field, that is less than ⅕ thearea of the irradiation field, or so forth. The energy degrader (orpieces thereof) may have a surface area that is less than twenty timesthe area of the particle beam spot at the irradiation field, that isless than fifteen times the area of the particle beam spot at theirradiation field, that is less than ten times the area of the particlebeam spot at the irradiation field, that is less than nine times thearea of the particle beam spot at the irradiation field, that is lessthan eight times the area of the particle beam spot at the irradiationfield, that is less than seven times the area of the particle beam spotat the irradiation field, that is less than six times the area of theparticle beam spot at the irradiation field, that is less than fivetimes the area of the particle beam spot at the irradiation field, thatis less than four times the area of the particle beam spot at theirradiation field, that is less than three times the area of theparticle beam spot at the irradiation field, or that is less than twotimes the area of the particle beam spot at the irradiation field. Insome implementations, the energy degrader (or pieces thereof) may have asurface area that is a multiple of the spot size, e.g., two times thespot size, three times the spot size, five times the spot size, tentimes the spot size, and so forth.

In some implementations, each piece (e.g., layer of multiple layers) hasa same size, shape, thickness and composition. In other implementations,different pieces may have different sizes, shapes thicknesses andcompositions.

The movement of the example energy degraders described herein may becontrolled in various ways. For example, the current through magnet 108may correspond to the deflection of the particle beam by the magnet and,thus, the location of the particle beam spot on the irradiation target.So, for example, knowing the current through the magnet and the locationof the irradiation target relative to the magnet, a computer systemcontrolling operation of the scanning system can determine the projectedlocation of the irradiation spot. And, knowing the location of theradiation spot, and the size of the energy degrader relative to the spotsize, the computer system can control the energy degrader, to track (ifnecessary) movement of the irradiation spot along all or part of itsmotion, as described herein.

The example movable energy degraders described herein may be mounted toone or more computer-controlled robotic arms or other structures thatalso contain elements of the scanning system to control movementrelative to the irradiation target. In implementations where the energydegrader includes more than one piece (e.g., multiple pieces or plates),there may be more than one robotic arm to independently control thedifferent pieces of the energy degrader in accordance with the treatmentplan. In some implementations, a single robotic arm may be configured tocontrol the different pieces independently.

Different cross-sections of the irradiation target may be scannedaccording to different treatment plans. As described above, an energydegrader is used to control the scanning depth. In some implementations,the particle beam may be interrupted or redirected during configurationof the energy degrader. In other implementations, this need not be thecase.

Described herein are examples of treating cross-sections of anirradiation target. These may be cross-sections that are roughlyperpendicular to the direction of the particle beam. However, theconcepts described herein are equally applicable to treating otherportions of an irradiation target that are not cross-sectionsperpendicular to the direction of the particle beam. For example, anirradiation target may be segmented into spherical, cubical or othershaped volumes, and those volumes may be treated using the exampleprocesses, systems, and/or devices described herein.

The processes described herein may be used with a single particleaccelerator, and any two or more of the features thereof describedherein may be used with the single particle accelerator. The particleaccelerator may be used in any type of medical or non-medicalapplication. An example of a particle therapy system that may be used isprovided below. Notably, the concepts described herein may be used inother systems not specifically described.

Referring to FIG. 23, an example implementation of a charged particleradiation therapy system 400 includes a beam-producing particleaccelerator 402 having a weight and size small enough to permit it to bemounted on a rotating gantry 404 with its output directed straight (thatis, essentially directly) from the accelerator housing toward a patient406. Particle accelerator 402 also includes a scanning system of a typedescribed herein (e.g., FIGS. 3 to 22).

In some implementations, the steel gantry has two legs 408, 410 mountedfor rotation on two respective bearings 412, 414 that lie on oppositesides of the patient. The accelerator is supported by a steel truss 416that is long enough to span a treatment area 418 in which the patientlies (e.g., twice as long as a tall person, to permit the person to berotated fully within the space with any desired target area of thepatient remaining in the line of the beam) and is attached stably atboth ends to the rotating legs of the gantry.

In some examples, the rotation of the gantry is limited to a range 420of less than 360 degrees, e.g., about 180 degrees, to permit a floor 422to extend from a wall of the vault 424 that houses the therapy systeminto the patient treatment area. The limited rotation range of thegantry also reduces the required thickness of some of the walls (whichare not directly aligned with the beam, e.g., wall 430), which provideradiation shielding of people outside the treatment area. A range of 180degrees of gantry rotation is enough to cover all treatment approachangles, but providing a larger range of travel can be useful. Forexample the range of rotation may be between 180 and 330 degrees andstill provide clearance for the therapy floor space. In otherimplementations, rotation is not limited as described above.

The horizontal rotational axis 432 of the gantry is located nominallyone meter above the floor where the patient and therapist interact withthe therapy system. This floor is positioned about 3 meters above thebottom floor of the therapy system shielded vault. The accelerator canswing under the raised floor for delivery of treatment beams from belowthe rotational axis. The patient couch moves and rotates in asubstantially horizontal plane parallel to the rotational axis of thegantry. The couch can rotate through a range 434 of about 270 degrees inthe horizontal plane with this configuration. This combination of gantryand patient rotational ranges and degrees of freedom allow the therapistto select virtually any approach angle for the beam. If needed, thepatient can be placed on the couch in the opposite orientation and thenall possible angles can be used.

In some implementations, the accelerator uses a synchrocyclotronconfiguration having a high magnetic field superconductingelectromagnetic structure. Because the bend radius of a charged particleof a given kinetic energy is reduced in direct proportion to an increasein the magnetic field applied to it, the high magnetic fieldsuperconducting magnetic structure permits the accelerator to be madesmaller and lighter. The synchrocyclotron uses a magnetic field that isuniform in rotation angle and falls off in strength with increasingradius. Such a field shape can be achieved regardless of the magnitudeof the magnetic field, so in theory there is no upper limit to themagnetic field strength (and therefore the resulting particle energy ata fixed radius) that can be used in a synchrocyclotron.

The synchrocyclotron is supported on the gantry so that the beam isgenerated directly in line with the patient. The gantry permits rotationof the synchrocyclotron about a horizontal rotational axis that containsa point (isocenter 440) within, or near, the patient. The split trussthat is parallel to the rotational axis, supports the synchrocyclotronon both sides.

Because the rotational range of the gantry is limited in some exampleimplementations, a patient support area can be accommodated in a widearea around the isocenter. Because the floor can be extended broadlyaround the isocenter, a patient support table can be positioned to moverelative to and to rotate about a vertical axis 442 through theisocenter so that, by a combination of gantry rotation and table motionand rotation, any angle of beam direction into any part of the patientcan be achieved. In some implementations, the two gantry arms areseparated by more than twice the height of a tall patient, allowing thecouch with patient to rotate and translate in a horizontal plane abovethe raised floor.

Limiting the gantry rotation angle allows for a reduction in thethickness of at least one of the walls surrounding the treatment room.Thick walls, typically constructed of concrete, provide radiationprotection to individuals outside the treatment room. A wall downstreamof a stopping proton beam may be about twice as thick as a wall at theopposite end of the room to provide an equivalent level of protection.Limiting the range of gantry rotation enables the treatment room to besited below earth grade on three sides, while allowing an occupied areaadjacent to the thinnest wall reducing the cost of constructing thetreatment room.

In the example implementation shown in FIG. 23, the superconductingsynchrocyclotron 402 operates with a peak magnetic field in a pole gapof the synchrocyclotron of 8.8 Tesla. The synchrocyclotron produces abeam of protons having an energy of 250 MeV. In some implementations,the synchrocyclotron is a variable-energy machine, and is capable ofoutputting proton beams having different energies. In someimplementations, the synchrocyclotron may produce a beam having a fixedenergy. In some implementations the field strength could be in the rangeof 4 T to 20 T and the proton energy could be in the range of 150 to 300MeV.

The radiation therapy system described in this example is used forproton radiation therapy, but the same principles and details can beapplied in analogous systems for use in heavy ion (ion) treatmentsystems.

As shown in FIGS. 1, 2, 24, 25, and 26, an example synchrocyclotron 10(e.g., 402 in FIG. 23) includes a magnet system 122 that contains aparticle source 190, a radiofrequency drive system 191, and a beamextraction system 318. In this example, the magnetic field establishedby the magnet system has a shape appropriate to maintain focus of acontained proton beam using a combination of a split pair of annularsuperconducting coils 140, 142 and a pair of shaped ferromagnetic (e.g.,low carbon steel) pole faces 144, 146.

The two superconducting magnet coils are centered on a common axis 147and are spaced apart along the axis. The coils may be formed by ofNb₃Sn-based superconducting 0.8 mm diameter strands (that initiallycomprise a niobium-tin core surrounded by a copper sheath) deployed in atwisted cable-in-channel conductor geometry. After seven individualstrands are cabled together, they are heated to cause a reaction thatforms the final (brittle) superconducting material of the wire. Afterthe material has been reacted, the wires are soldered into the copperchannel (outer dimensions 3.18×2.54 mm and inner dimensions 2.08×2.08mm) and covered with insulation (in this example, a woven fiberglassmaterial). The copper channel containing the wires is then wound in acoil having a rectangular cross-section. The wound coil is then vacuumimpregnated with an epoxy compound. The finished coils are mounted on anannular stainless steel reverse bobbin. Heater blankets may be placed atintervals in the layers of the windings to protect the assembly in theevent of a magnet quench.

The entire coil can then be covered with copper sheets to providethermal conductivity and mechanical stability and then contained in anadditional layer of epoxy. The precompression of the coil can beprovided by heating the stainless steel reverse bobbin and fitting thecoils within the reverse bobbin. The reverse bobbin inner diameter ischosen so that when the entire mass is cooled to 4 K, the reverse bobbinstays in contact with the coil and provides some compression. Heatingthe stainless steel reverse bobbin to approximately 50 degrees C. andfitting coils at a temperature of 100 degrees Kelvin can achieve this.

The geometry of the coil is maintained by mounting the coils in a“reverse” rectangular bobbin to exert a restorative force that worksagainst the distorting force produced when the coils are energized. Asshown in FIG. 25, in some implementations, coil position is maintainedrelative to corresponding magnet pole pieces and the cryostat using aset of warm-to-cold support straps 402, 404, 406. Supporting the coldmass with thin straps reduces the heat leakage imparted to the cold massby the rigid support system. The straps are arranged to withstand thevarying gravitational force on the coil as the magnet rotates on boardthe gantry. They withstand the combined effects of gravity and the largede-centering force realized by the coil when it is perturbed from aperfectly symmetric position relative to the magnet yoke. Additionallythe links act to reduce dynamic forces imparted on the coil as thegantry accelerates and decelerates when its position is changed. Eachwarm-to-cold support may include one S2 fiberglass link and one carbonfiber link. The carbon fiber link is supported across pins between thewarm yoke and an intermediate temperature (50-70 K), and the S2fiberglass link 408 is supported across the intermediate temperature pinand a pin attached to the cold mass. Each pin may be made of highstrength stainless steel.

Referring to FIG. 1, the field strength profile as a function of radiusis determined largely by choice of coil geometry and pole face shape;the pole faces 144, 146 of the permeable yoke material can be contouredto fine tune the shape of the magnetic field to ensure that the particlebeam remains focused during acceleration.

The superconducting coils are maintained at temperatures near absolutezero (e.g., about 4 degrees Kelvin) by enclosing the coil assembly (thecoils and the bobbin) inside an evacuated annular aluminum or stainlesssteel cryostatic chamber 170 (the cryostat) that provides a free spacearound the coil structure, except at a limited set of support points171, 173. In an alternate version (e.g., FIG. 2) the outer wall of thecryostat may be made of low carbon steel to provide an additional returnflux path for the magnetic field.

In some implementations, the temperature near absolute zero is achievedand maintained using one single-stage Gifford-McMahon cryo-cooler andthree two-stage Gifford McMahon cryo-coolers. Each two stage cryo-coolerhas a second stage cold end attached to a condenser that recondensesHelium vapor into liquid Helium. In some implementations, thetemperature near absolute zero is achieved and maintained using acooling channel (not shown) containing liquid helium, which is formedinside a superconducting coil support structure (e.g., the reversebobbin), and which contains a thermal connection between the liquidhelium in the channel and the corresponding superconducting coil. Anexample of a liquid helium cooling system of the type described above,and that may be used is described in U.S. patent application Ser. No.13/148,000 (Begg et al.).

In some implementations, the coil assembly and cryostatic chambers aremounted within and fully enclosed by two halves 181, 183 of apillbox-shaped magnet yoke 100. The yoke 100 provides a path for thereturn magnetic field flux 184 and magnetically shields the volume 186between the pole faces 144, 146 to prevent external magnetic influencesfrom perturbing the shape of the magnetic field within that volume. Theyoke also serves to decrease the stray magnetic field in the vicinity ofthe accelerator. In other implementations, the coil assembly andcryostatic chambers are mounted within and fully enclosed by anon-magnetic enclosure, and the path for return magnetic field flux isimplemented using an active return system, an example of which isdescribed above.

As shown in FIGS. 1 and 27, the synchrocyclotron includes a particlesource 190 of a Penning ion gauge geometry located near the geometriccenter 192 of the magnet structure 182. The particle source may be asdescribed below, or the particle source may be of the type described inU.S. patent application Ser. No. 11/948,662 incorporated herein byreference.

Particle source 190 is fed from a supply 399 of hydrogen through a gasline 393 and tube 394 that delivers gaseous hydrogen. Electric cables294 carry an electric current from a current source to stimulateelectron discharge from cathodes 392, 390 that are aligned with themagnetic field 400.

In this example, the discharged electrons ionize the gas exiting througha small hole from tube 394 to create a supply of positive ions (protons)for acceleration by one semicircular (dee-shaped) radio-frequency platethat spans half of the space enclosed by the magnet structure and onedummy dee plate. In the case of an interrupted particle source (anexample of which is described in U.S. patent application Ser. No.11/948,662), all (or a substantial part, e.g., a majority) of the tubecontaining plasma is removed at the acceleration region.

As shown in FIG. 28, the dee plate 500 is a hollow metal structure thathas two semicircular surfaces 503, 505 that enclose a space 507 in whichthe protons are accelerated during half of their rotation around thespace enclosed by the magnet structure. A duct 509 opening into thespace 507 extends through the enclosure (e.g., the yoke or polepiece(s)) to an external location from which a vacuum pump can beattached to evacuate the space 507 and the rest of the space within avacuum chamber in which the acceleration takes place. The dummy dee 502comprises a rectangular metal ring that is spaced near to the exposedrim of the dee plate. The dummy dee is grounded to the vacuum chamberand magnet yoke. The dee plate 500 is driven by a radio-frequency signalthat is applied at the end of a radio-frequency transmission line toimpart an electric field in the space 507. The radio frequency electricfield is made to vary in time as the accelerated particle beam increasesin distance from the geometric center. The radio frequency electricfield may be controlled in the manner described in U.S. patentapplication Ser. No. 11/948,359, entitled “Matching A Resonant FrequencyOf A Resonant Cavity To A Frequency Of An Input Voltage”, the contentsof which are incorporated herein by reference.

For the beam emerging from the centrally located particle source toclear the particle source structure as it begins to spiral outward, alarge voltage difference may be applied across the radio frequencyplates. 20,000 Volts is applied across the radio frequency plates. Insome versions from 8,000 to 20,000 Volts may be applied across the radiofrequency plates. To reduce the power required to drive this largevoltage, the magnet structure is arranged to reduce the capacitancebetween the radio frequency plates and ground. This may be done byforming holes with sufficient clearance from the radio frequencystructures through the outer yoke and the cryostat housing and makingsufficient space between the magnet pole faces.

The high voltage alternating potential that drives the dee plate has afrequency that is swept downward during the accelerating cycle toaccount for the increasing relativistic mass of the protons and thedecreasing magnetic field. The dummy dee does not require a hollowsemi-cylindrical structure as it is at ground potential along with thevacuum chamber walls. Other plate arrangements could be used such asmore than one pair of accelerating electrodes driven with differentelectrical phases or multiples of the fundamental frequency. The RFstructure can be tuned to keep the Q high during the required frequencysweep by using, for example, a rotating capacitor having intermeshingrotating and stationary blades. During each meshing of the blades, thecapacitance increases, thus lowering the resonant frequency of the RFstructure. The blades can be shaped to create a precise frequency sweeprequired. A drive motor for the rotating condenser can be phase lockedto the RF generator for precise control. One bunch of particles may beaccelerated during each meshing of the blades of the rotating condenser.

The vacuum chamber in which the acceleration occurs is a generallycylindrical container that is thinner in the center and thicker at therim. The vacuum chamber encloses the RF plates and the particle sourceand is evacuated by a vacuum pump. Maintaining a high vacuum reduces thechances that accelerating ions are not lost to collisions with gasmolecules and enables the RF voltage to be kept at a higher levelwithout arcing to ground.

Protons (or other ions) traverse a generally spiral orbital pathbeginning at the particle source. In half of each loop of the spiralpath, the protons gain energy as they pass through the RF electricfield. As the protons gain energy, the radius of the central orbit ofeach successive loop of their spiral path is larger than the prior loopuntil the loop radius reaches the maximum radius of the pole face. Atthat location a magnetic and electric field perturbation directs protonsinto an area where the magnetic field rapidly decreases, and the protonsdepart the area of the high magnetic field and are directed through anevacuated tube, referred to herein as the extraction channel, to exitthe synchrocyclotron. A magnetic regenerator may be used to change themagnetic field perturbation to direct the protons. The protons exitingwill tend to disperse as they enter an area of markedly decreasedmagnetic field that exists in the room around the synchrocyclotron. Beamshaping elements 607, 609 in the extraction channel 138 (FIG. 25)redirect the protons so that they stay in a straight beam of limitedspatial extent.

As the beam exits the extraction channel it is passed through a beamformation system 525 (FIG. 25), which may include a scanning system ofthe type described herein. Beam formation system 525 may be used inconjunction with an inner gantry that controls application of the beam.

Stray magnetic fields exiting from the synchrocyclotron may be limitedby both a magnet yoke (which also serves as a shield) and a separatemagnetic shield 514 (e.g., FIG. 1). The separate magnetic shieldincludes of a layer 517 of ferromagnetic material (e.g., steel or iron)that encloses the pillbox yoke, separated by a space 516. Thisconfiguration that includes a sandwich of a yoke, a space, and a shieldachieves adequate shielding for a given leakage magnetic field at lowerweight. As described above, in some implementations, an active returnsystem may be used in place of, or to augment, the operation of themagnetic yoke and shield.

Referring to FIG. 23, the gantry allows the synchrocyclotron to berotated about a horizontal rotational axis 432. The truss structure 416has two generally parallel spans 480, 482. The synchrocyclotron iscradled between the spans about midway between the legs. The gantry isbalanced for rotation about the bearings using counterweights 622, 624mounted on ends of the legs opposite the truss.

The gantry is driven to rotate by an electric motor mounted to one orboth of the gantry legs and connected to the bearing housings by drivegears. The rotational position of the gantry is derived from signalsprovided by shaft angle encoders incorporated into the gantry drivemotors and the drive gears.

At the location at which the ion beam exits the synchrocyclotron, thebeam formation system 525 acts on the ion beam to give it propertiessuitable for patient treatment. For example, the beam may be spread andits depth of penetration varied to provide uniform radiation across agiven target volume. The beam formation system may include activescanning elements as described herein.

All of the active systems of the synchrocyclotron (the current drivensuperconducting coils, the RF-driven plates, the vacuum pumps for thevacuum acceleration chamber and for the superconducting coil coolingchamber, the current driven particle source, the hydrogen gas source,and the RF plate coolers, for example), may be controlled by appropriatesynchrocyclotron control electronics (not shown), which may include,e.g., one or more processing devices executing instructions from memoryto effect control.

As explained above, referring to system 602 of FIG. 29, a beam-producingparticle accelerator, in this case synchrocyclotron 604 (which mayinclude any and all features described herein), may be mounted onrotating gantry 605. Rotating gantry 605 is of the type describedherein, and can angularly rotate around patient support 606. Thisfeature enables synchrocyclotron 604 to provide a particle beamessentially directly to the patient from various angles. For example, asin FIG. 29, if synchrocyclotron 604 is above patient support 606, theparticle beam may be directed downwards toward the patient.Alternatively, if synchrocyclotron 604 is below patient support 606, theparticle beam may be directed upwards toward the patient. The particlebeam is applied essentially directly to the patient in the sense that anintermediary beam routing mechanism is not required. A routingmechanism, in this context, is different from a shaping or sizingmechanism in that a shaping or sizing mechanism does not re-route thebeam, but rather sizes and/or shapes the beam while maintaining the samegeneral trajectory of the beam.

Further details regarding an example implementation of the foregoingsystem may be found in U.S. Pat. No. 7,728,311, filed on Nov. 16, 2006and entitled “Charged Particle Radiation Therapy”, and in U.S. patentapplication Ser. No. 12/275,103, filed on Nov. 20, 2008 and entitled“Inner Gantry”. The contents of U.S. Pat. No. 7,728,311 and in U.S.patent application Ser. No. 12/275,103 are hereby incorporated byreference into this disclosure. In some implementations, thesynchrocyclotron may be a variable-energy device, such as that describedin U.S. patent application Ser. No. 13/916,401, filed on Jun. 12, 2013,the contents of which are incorporated herein by reference.

Variable-Energy Particle Accelerator

The particle accelerator used in the example particle therapy systemsand example scanning systems described herein may be a variable-energyparticle accelerator, an example of which is described below

The energy of an extracted particle beam (the particle beam output fromthe accelerator) can affect the use of the particle beam duringtreatment. In some machines, the energy of the particle beam (orparticles in the particle beam) does not increase after extraction.However, the energy may be reduced based on treatment needs after theextraction and before the treatment. Referring to FIG. 30, an exampletreatment system 910 includes an accelerator 912, e.g., asynchrocyclotron, from which a particle (e.g., proton) beam 914 having avariable energy is extracted to irradiate a target volume 924 of a body922. Optionally, one or more additional devices, such as a scanning unit916 or a scattering unit 916, one or more monitoring units 918, and anenergy degrader 920, are placed along the irradiation direction 928. Thedevices intercept the cross-section of the extracted beam 914 and alterone or more properties of the extracted beam for the treatment.

A target volume to be irradiated (an irradiation target) by a particlebeam for treatment typically has a three-dimensional configuration. Insome examples, to carry-out the treatment, the target volume is dividedinto layers along the irradiation direction of the particle beam so thatthe irradiation can be done on a layer-by-layer basis. For certain typesof particles, such as protons, the penetration depth (or which layer thebeam reaches) within the target volume is largely determined by theenergy of the particle beam. A particle beam of a given energy does notreach substantially beyond a corresponding penetration depth for thatenergy. To move the beam irradiation from one layer to another layer ofthe target volume, the energy of the particle beam is changed.

In the example shown in FIG. 30, the target volume 924 is divided intonine layers 926 a-926 i along the irradiation direction 928. In anexample process, the irradiation starts from the deepest layer 926 i,one layer at a time, gradually to the shallower layers and finishes withthe shallowest layer 926 a. Before application to the body 922, theenergy of the particle beam 914 is controlled to be at a level to allowthe particle beam to stop at a desired layer, e.g., the layer 926 d,without substantially penetrating further into the body or the targetvolume, e.g., the layers 926 e-926 i or deeper into the body. In someexamples, the desired energy of the particle beam 914 decreases as thetreatment layer becomes shallower relative to the particle acceleration.In some examples, the beam energy difference for treating adjacentlayers of the target volume 924 is about 3 MeV to about 100 MeV, e.g.,about 10 MeV to about 80 MeV, although other differences may also bepossible, depending on, e.g., the thickness of the layers and theproperties of the beam.

The energy variation for treating different layers of the target volume924 can be performed at the accelerator 912 (e.g., the accelerator canvary the energy) so that, in some implementations, no additional energyvariation is required after the particle beam is extracted from theaccelerator 912. So, the optional energy degrader 920 in the treatmentsystem 10 may be eliminated from the system. In some implementations,the accelerator 912 can output particle beams having an energy thatvaries between about 100 MeV and about 300 MeV, e.g., between about 115MeV and about 250 MeV. The variation can be continuous ornon-continuous, e.g., one step at a time. In some implementations, thevariation, continuous or non-continuous, can take place at a relativelyhigh rate, e.g., up to about 50 MeV per second or up to about 20 MeV persecond. Non-continuous variation can take place one step at a time witha step size of about 10 MeV to about 90 MeV.

When irradiation is complete in one layer, the accelerator 912 can varythe energy of the particle beam for irradiating a next layer, e.g.,within several seconds or within less than one second. In someimplementations, the treatment of the target volume 924 can be continuedwithout substantial interruption or even without any interruption. Insome situations, the step size of the non-continuous energy variation isselected to correspond to the energy difference needed for irradiatingtwo adjacent layers of the target volume 924. For example, the step sizecan be the same as, or a fraction of, the energy difference.

In some implementations, the accelerator 912 and the degrader 920collectively vary the energy of the beam 914. For example, theaccelerator 912 provides a coarse adjustment and the degrader 920provides a fine adjustment or vice versa. In this example, theaccelerator 912 can output the particle beam that varies energy with avariation step of about 10-80 MeV, and the degrader 920 adjusts (e.g.,reduces) the energy of the beam at a variation step of about 2-10 MeV.

The reduced use (or absence) of the energy degrader, such as a rangemodulator, may help to maintain properties and quality of the outputbeam from the accelerator, e.g., beam intensity. The control of theparticle beam can be performed at the accelerator. Side effects, e.g.,from neutrons generated when the particle beam passes the degrader 920can be reduced or eliminated.

The energy of the particle beam 914 may be adjusted to treat anothertarget volume 930 in another body or body part 922′ after completingtreatment in target volume 924. The target volumes 924, 930 may be inthe same body (or patient), or in different patients. It is possiblethat the depth D of the target volume 930 from a surface of body 922′ isdifferent from that of the target volume 924. Although some energyadjustment may be performed by the degrader 920, the degrader 912 mayonly reduce the beam energy and not increase the beam energy.

In this regard, in some cases, the beam energy required for treatingtarget volume 930 is greater than the beam energy required to treattarget volume 924. In such cases, the accelerator 912 may increase theoutput beam energy after treating the target volume 924 and beforetreating the target volume 930. In other cases, the beam energy requiredfor treating target volume 930 is less than the beam energy required totreat target volume 924. Although the degrader 920 can reduce theenergy, the accelerator 912 can be adjusted to output a lower beamenergy to reduce or eliminate the use of the degrader 920. The divisionof the target volumes 924, 930 into layers can be different or the same.The target volume 930 can be treated similarly on a layer by layer basisto the treatment of the target volume 924.

The treatment of the different target volumes 924, 930 on the samepatient may be substantially continuous, e.g., with the stop timebetween the two volumes being no longer than about 30 minutes or less,e.g., 25 minutes or less, 20 minutes or less, 15 minutes or less, 10minutes or less, 5 minutes or less, or 1 minute or less. As explainedherein, the accelerator 912 can be mounted on a movable gantry and themovement of the gantry can move the accelerator to aim at differenttarget volumes. In some situations, the accelerator 912 can complete theenergy adjustment of the output beam 914 during the time the treatmentsystem makes adjustment (such as moving the gantry) after completing thetreatment of the target volume 924 and before starting treating thetarget volume 930. After the alignment of the accelerator and the targetvolume 930, the treatment can begin with the adjusted, desired beamenergy. Beam energy adjustment for different patients can also becompleted relatively efficiently. In some examples, all adjustments,including increasing/reducing beam energy and/or moving the gantry aredone within about 30 minutes, e.g., within about 25 minutes, withinabout 20 minutes, within about 15 minutes, within about 10 minutes orwithin about 5 minutes.

In the same layer of a target volume, an irradiation dose may be appliedby moving the beam across the two-dimensional surface of the layer(which is sometimes called scanning beam) using a scanning unit 916.Alternatively, the layer can be irradiated by passing the extracted beamthrough one or more scatterers of the scattering unit 16 (which issometimes called scattering beam).

Beam properties, such as energy and intensity, can be selected before atreatment or can be adjusted during the treatment by controlling theaccelerator 912 and/or other devices, such as the scanningunit/scatterer(s) 916, the degrader 920, and others not shown in thefigures. In example implementations, system 910 includes a controller932, such as a computer, in communication with one or more devices inthe system. Control can be based on results of the monitoring performedby the one or more monitors 918, e.g., monitoring of the beam intensity,dose, beam location in the target volume, etc. Although the monitors 918are shown to be between the device 916 and the degrader 920, one or moremonitors can be placed at other appropriate locations along the beamirradiation path. Controller 932 can also store a treatment plan for oneor more target volumes (for the same patient and/or different patients).The treatment plan can be determined before the treatment starts and caninclude parameters, such as the shape of the target volume, the numberof irradiation layers, the irradiation dose for each layer, the numberof times each layer is irradiated, etc. The adjustment of a beamproperty within the system 910 can be performed based on the treatmentplan. Additional adjustment can be made during the treatment, e.g., whendeviation from the treatment plan is detected.

In some implementations, the accelerator 912 is configured to vary theenergy of the output particle beam by varying the magnetic field inwhich the particle beam is accelerated. In an example implementation,one or more sets of coils receives variable electrical current toproduce a variable magnetic field in the cavity. In some examples, oneset of coils receives a fixed electrical current, while one or moreother sets of coils receives a variable current so that the totalcurrent received by the coil sets varies. In some implementations, allsets of coils are superconducting. In other implementations, some setsof coils, such as the set for the fixed electrical current, aresuperconducting, while other sets of coils, such as the one or more setsfor the variable current, are non-superconducting. In some examples, allsets of coils are non-superconducting.

Generally, the magnitude of the magnetic field is scalable with themagnitude of the electrical current. Adjusting the total electriccurrent of the coils in a predetermined range can generate a magneticfield that varies in a corresponding, predetermined range. In someexamples, a continuous adjustment of the electrical current can lead toa continuous variation of the magnetic field and a continuous variationof the output beam energy. Alternatively, when the electrical currentapplied to the coils is adjusted in a non-continuous, step-wise manner,the magnetic field and the output beam energy also varies accordingly ina non-continuous (step-wise) manner. The scaling of the magnetic fieldto the current can allow the variation of the beam energy to be carriedout relatively precisely, although sometimes minor adjustment other thanthe input current may be performed.

In some implementations, to output particle beams having a variableenergy, the accelerator 912 is configured to apply RF voltages thatsweep over different ranges of frequencies, with each rangecorresponding to a different output beam energy. For example, if theaccelerator 912 is configured to produce three different output beamenergies, the RF voltage is capable of sweeping over three differentranges of frequencies. In another example, corresponding to continuousbeam energy variations, the RF voltage sweeps over frequency ranges thatcontinuously change. The different frequency ranges may have differentlower frequency and/or upper frequency boundaries.

The extraction channel may be configured to accommodate the range ofdifferent energies produced by the variable-energy particle accelerator.For example the extraction channel may be large enough to support thehighest and lowest energies produced by the particle accelerator. Thatis, the extraction channel may be sized or otherwise configured toreceive and to transmit particles within that range of energies.Particle beams having different energies can be extracted from theaccelerator 912 without altering the features of the regenerator that isused for extracting particle beams having a single energy. In otherimplementations, to accommodate the variable particle energy, theregenerator can be moved to disturb (e.g., change) different particleorbits in the manner described above and/or iron rods (magnetic shims)can be added or removed to change the magnetic field bump provided bythe regenerator. More specifically, different particle energies willtypically be at different particle orbits within the cavity. By movingthe regenerator, it is possible to intercept a particle orbit at aspecified energy and thereby provide the correct perturbation of thatorbit so that particles at the specified energy reach the extractionchannel. In some implementations, movement of the regenerator (and/oraddition/removal of magnetic shims) is performed in real-time to matchreal-time changes in the particle beam energy output by the accelerator.In other implementations, particle energy is adjusted on a per-treatmentbasis, and movement of the regenerator (and/or addition/removal ofmagnetic shims) is performed in advance of the treatment. In eithercase, movement of the regenerator (and/or addition/removal of magneticshims) may be computer controlled. For example, a computer may controlone or more motors that effect movement of the regenerator and/ormagnetic shims.

In some implementations, the regenerator is implemented using one ormore magnetic shims that are controllable to move to the appropriatelocation(s).

As an example, table 1 shows three example energy levels at whichexample accelerator 912 can output particle beams. The correspondingparameters for producing the three energy levels are also listed. Inthis regard, the magnet current refers to the total electrical currentapplied to the one or more coil sets in the accelerator 912; the maximumand minimum frequencies define the ranges in which the RF voltagesweeps; and “r” is the radial distance of a location to a center of thecavity in which the particles are accelerated.

TABLE 1 Examples of beam energies and respective parameters. MagneticMagnetic Beam Magnet Maximum Minimum Field at Field at Energy CurrentFrequency Frequency r = 0 mm r = 298 mm (MeV) (Amps) (MHz) (MHz) (Tesla)(Tesla) 250 1990 132 99 8.7 8.2 235 1920 128 97 8.4 8.0 211 1760 120 937.9 7.5

Details that may be included in an example particle accelerator thatproduces charged particles having variable energies are described below.The accelerator can be a synchrocyclotron and the particles may beprotons. The particles may be output as pulsed beams. The energy of thebeam output from the particle accelerator can be varied during thetreatment of one target volume in a patient, or between treatments ofdifferent target volumes of the same patient or different patients. Insome implementations, settings of the accelerator are changed to varythe beam energy when no beam (or particles) is output from theaccelerator. The energy variation can be continuous or non-continuousover a desired range.

Referring to the example shown in FIG. 1, the particle accelerator(e.g., synchrocyclotron 502), which may be a variable-energy particleaccelerator like accelerator 912 described above, may be configured tooutput particle beams that have a variable energy. The range of thevariable energy can have an upper boundary that is about 200 MeV toabout 300 MeV or higher, e.g., 200 MeV, about 205 MeV, about 210 MeV,about 215 MeV, about 220 MeV, about 225 MeV, about 230 MeV, about 235MeV, about 240 MeV, about 245 MeV, about 250 MeV, about 255 MeV, about260 MeV, about 265 MeV, about 270 MeV, about 275 MeV, about 280 MeV,about 285 MeV, about 290 MeV, about 295 MeV, or about 300 MeV or higher.The range can also have a lower boundary that is about 100 MeV or lowerto about 200 MeV, e.g., about 100 MeV or lower, about 105 MeV, about 110MeV, about 115 MeV, about 120 MeV, about 125 MeV, about 130 MeV, about135 MeV, about 140 MeV, about 145 MeV, about 150 MeV, about 155 MeV,about 160 MeV, about 165 MeV, about 170 MeV, about 175 MeV, about 180MeV, about 185 MeV, about 190 MeV, about 195 MeV, about 200 MeV.

In some examples, the variation is non-continuous and the variation stepcan have a size of about 10 MeV or lower, about 15 MeV, about 20 MeV,about 25 MeV, about 30 MeV, about 35 MeV, about 40 MeV, about 45 MeV,about 50 MeV, about 55 MeV, about 60 MeV, about 65 MeV, about 70 MeV,about 75 MeV, or about 80 MeV or higher. Varying the energy by one stepsize can take no more than 30 minutes, e.g., about 25 minutes or less,about 20 minutes or less, about 15 minutes or less, about 10 minutes orless, about 5 minutes or less, about 1 minute or less, or about 30seconds or less. In other examples, the variation is continuous and theaccelerator can adjust the energy of the particle beam at a relativelyhigh rate, e.g., up to about 50 MeV per second, up to about 45 MeV persecond, up to about 40 MeV per second, up to about 35 MeV per second, upto about 30 MeV per second, up to about 25 MeV per second, up to about20 MeV per second, up to about 15 MeV per second, or up to about 10 MeVper second. The accelerator can be configured to adjust the particleenergy both continuously and non-continuously. For example, acombination of the continuous and non-continuous variation can be usedin a treatment of one target volume or in treatments of different targetvolumes. Flexible treatment planning and flexible treatment can beachieved.

A particle accelerator that outputs a particle beam having a variableenergy can provide accuracy in irradiation treatment and reduce thenumber of additional devices (other than the accelerator) used for thetreatment. For example, the use of degraders for changing the energy ofan output particle beam may be reduced or eliminated for all or part ofthe treatment. The properties of the particle beam, such as intensity,focus, etc. can be controlled at the particle accelerator and theparticle beam can reach the target volume without substantialdisturbance from the additional devices. The relatively high variationrate of the beam energy can reduce treatment time and allow forefficient use of the treatment system.

In some implementations, the accelerator, such as the synchrocyclotron502 of FIG. 1, accelerates particles or particle beams to variableenergy levels by varying the magnetic field in the accelerator, whichcan be achieved by varying the electrical current applied to coils forgenerating the magnetic field. As explained above, an examplesynchrocyclotron (e.g., 502 in FIG. 1) includes a magnet system thatcontains a particle source, a radiofrequency drive system, and a beamextraction system. FIG. 33 shows an example of a magnet system that maybe used in a variable-energy accelerator. In this exampleimplementation, the magnetic field established by the magnet system 1012can vary by about 5% to about 35% of a maximum value of the magneticfield that two sets of coils 40 a and 40 b, and 42 a and 42 b arecapable of generating. The magnetic field established by the magnetsystem has a shape appropriate to maintain focus of a contained protonbeam using a combination of the two sets of coils and a pair of shapedferromagnetic (e.g., low carbon steel) structures, examples of which areprovided above.

Each set of coils may be a split pair of annular coils to receiveelectrical current. In some situations, both sets of coils aresuperconducting. In other situations, only one set of the coils issuperconducting and the other set is non-superconducting or normalconducting (also discussed further below). It is also possible that bothsets of coils are non-superconducting. Suitable superconductingmaterials for use in the coils include niobium-3 tin (Nb3 Sn) and/orniobium-titanium. Other normal conducting materials can include copper.Examples of the coil set constructions are described further below.

The two sets of coils can be electrically connected serially or inparallel. In some implementations, the total electrical current receivedby the two sets of coils can include about 2 million ampere turns toabout 10 million ampere turns, e.g., about 2.5 to about 7.5 millionampere turns or about 3.75 million ampere turns to about 5 millionampere turns. In some examples, one set of coils is configured toreceive a fixed (or constant) portion of the total variable electricalcurrent, while the other set of coils is configured to receive avariable portion of the total electrical current. The total electricalcurrent of the two coil sets varies with the variation of the current inone coil set. In other situations, the electrical current applied toboth sets of coils can vary. The variable total current in the two setsof coils can generate a magnetic field having a variable magnitude,which in turn varies the acceleration pathways of the particles andproduces particles having variable energies.

Generally, the magnitude of the magnetic field generated by the coil(s)is scalable to the magnitude of the total electrical current applied tothe coil(s). Based on the scalability, in some implementations, linearvariation of the magnetic field strength can be achieved by linearlychanging the total current of the coil sets. The total current can beadjusted at a relatively high rate that leads to a relatively high-rateadjustment of the magnetic field and the beam energy.

In the example reflected in Table 1 above, the ratio between values ofthe current and the magnetic field at the geometric center of the coilrings is: 1990:8.7 (approximately 228.7:1); 1920:8.4 (approximately228.6:1); 1760:7.9 (approximately 222.8:1). Accordingly, adjusting themagnitude of the total current applied to a superconducting coil(s) canproportionally (based on the ratio) adjust the magnitude of the magneticfield.

The scalability of the magnetic field to the total electrical current inthe example of Table 1 is also shown in the plot of FIG. 31, where BZ isthe magnetic field along the Z direction; and R is the radial distancemeasured from a geometric center of the coil rings along a directionperpendicular to the Z direction. The magnetic field has the highestvalue at the geometric center, and decreases as the distance Rincreases. The curves 1035, 1037 represent the magnetic field generatedby the same coil sets receiving different total electrical current: 1760Amperes and 1990 Amperes, respectively. The corresponding energies ofthe extracted particles are 211 MeV and 250 MeV, respectively. The twocurves 1035, 1037 have substantially the same shape and the differentparts of the curves 1035, 1037 are substantially parallel. As a result,either the curve 1035 or the curve 1037 can be linearly shifted tosubstantially match the other curve, indicating that the magnetic fieldis scalable to the total electrical current applied to the coil sets.

In some implementations, the scalability of the magnetic field to thetotal electrical current may not be perfect. For example, the ratiobetween the magnetic field and the current calculated based on theexample shown in table 1 is not constant. Also, as shown in FIG. 31, thelinear shift of one curve may not perfectly match the other curve. Insome implementations, the total current is applied to the coil setsunder the assumption of perfect scalability. The target magnetic field(under the assumption of perfect scalability) can be generated byadditionally altering the features, e.g., geometry, of the coils tocounteract the imperfection in the scalability. As one example,ferromagnetic (e.g., iron) rods (magnetic shims) can be inserted orremoved from one or both of the magnetic structures (e.g., yokes, polepieces, and the like). The features of the coils can be altered at arelatively high rate so that the rate of the magnetic field adjustmentis not substantially affected as compared to the situation in which thescalability is perfect and only the electrical current needs to beadjusted. In the example of iron rods, the rods can be added or removedat the time scale of seconds or minutes, e.g., within 5 minutes, within1 minute, less than 30 seconds, or less than 1 second.

In some implementations, settings of the accelerator, such as thecurrent applied to the coil sets, can be chosen based on the substantialscalability of the magnetic field to the total electrical current in thecoil sets.

Generally, to produce the total current that varies within a desiredrange, any appropriate combination of current applied to the two coilsets can be used. In an example, the coil set 42 a, 42 b can beconfigured to receive a fixed electrical current corresponding to alower boundary of a desired range of the magnetic field. In the exampleshown in table 1, the fixed electrical current is 1760 Amperes. Inaddition, the coil set 40 a, 40 b can be configured to receive avariable electrical current having an upper boundary corresponding to adifference between an upper boundary and a lower boundary of the desiredrange of the magnetic field. In the example shown in table 1, the coilset 40 a, 40 b is configured to receive electrical current that variesbetween 0 Ampere and 230 Amperes.

In another example, the coil set 42 a, 42 b can be configured to receivea fixed electrical current corresponding to an upper boundary of adesired range of the magnetic field. In the example shown in table 1,the fixed current is 1990 Amperes. In addition, the coil set 40 a, 40 bcan be configured to receive a variable electrical current having anupper boundary corresponding to a difference between a lower boundaryand an upper boundary of the desired range of the magnetic field. In theexample shown in table 1, the coil set 40 a, 40 b is configured toreceive electrical current that varies between −230 Ampere and 0 Ampere.

The total variable magnetic field generated by the variable totalcurrent for accelerating the particles can have a maximum magnitudegreater than 4 Tesla, e.g., greater than 5 Tesla, greater than 6 Tesla,greater than 7 Tesla, greater than 8 Tesla, greater than 9 Tesla, orgreater than 10 Tesla, and up to about 20 Tesla or higher, e.g., up toabout 18 Tesla, up to about 15 Tesla, or up to about 12 Tesla. In someimplementations, variation of the total current in the coil sets canvary the magnetic field by about 0.2 Tesla to about 4.2 Tesla or more,e.g., about 0.2 Tesla to about 1.4 Tesla or about 0.6 Tesla to about 4.2Tesla. In some situations, the amount of variation of the magnetic fieldcan be proportional to the maximum magnitude.

FIG. 32 shows an example RF structure for sweeping the voltage on thedee plate 500 over an RF frequency range for each energy level of theparticle beam, and for varying the frequency range when the particlebeam energy is varied. The semicircular surfaces 503, 505 of the deeplate 500 are connected to an inner conductor 1300 and housed in anouter conductor 1302. The high voltage is applied to the dee plate 500from a power source (not shown, e.g., an oscillating voltage input)through a power coupling device 1304 that couples the power source tothe inner conductor. In some implementations, the coupling device 1304is positioned on the inner conductor 1300 to provide power transfer fromthe power source to the dee plate 500. In addition, the dee plate 500 iscoupled to variable reactive elements 1306, 1308 to perform the RFfrequency sweep for each particle energy level, and to change the RFfrequency range for different particle energy levels.

The variable reactive element 1306 can be a rotating capacitor that hasmultiple blades 1310 rotatable by a motor (not shown). By meshing orunmeshing the blades 1310 during each cycle of RF sweeping, thecapacitance of the RF structure changes, which in turn changes theresonant frequency of the RF structure. In some implementations, duringeach quarter cycle of the motor, the blades 1310 mesh with the eachother. The capacitance of the RF structure increases and the resonantfrequency decreases. The process reverses as the blades 1310 unmesh. Asa result, the power required to generate the high voltage applied to thedee plate 103 and necessary to accelerate the beam can be reduced by alarge factor. In some implementations, the shape of the blades 1310 ismachined to form the required dependence of resonant frequency on time.

The RF frequency generation is synchronized with the blade rotation bysensing the phase of the RF voltage in the resonator, keeping thealternating voltage on the dee plates close to the resonant frequency ofthe RF cavity. (The dummy dee is grounded and is not shown in FIG. 32).

The variable reactive element 1308 can be a capacitor formed by a plate1312 and a surface 1316 of the inner conductor 1300. The plate 1312 ismovable along a direction 1314 towards or away from the surface 1316.The capacitance of the capacitor changes as the distance D between theplate 1312 and the surface 1316 changes. For each frequency range to beswept for one particle energy, the distance D is at a set value, and tochange the frequency range, the plate 1312 is moved corresponding to thechange in the energy of the output beam.

In some implementations, the inner and outer conductors 1300, 1302 areformed of a metallic material, such as copper, aluminum, or silver. Theblades 1310 and the plate 1312 can also be formed of the same ordifferent metallic materials as the conductors 1300, 1302. The couplingdevice 1304 can be an electrical conductor. The variable reactiveelements 1306, 1308 can have other forms and can couple to the dee plate100 in other ways to perform the RF frequency sweep and the frequencyrange alteration. In some implementations, a single variable reactiveelement can be configured to perform the functions of both the variablereactive elements 1306, 1308. In other implementations, more than twovariable reactive elements can be used.

The control of the gantry, the patient support, the active beam shapingelements, and the synchrocyclotron to perform a therapy session isachieved by appropriate therapy control electronics (not shown).

Control of the particle therapy system described herein and its variousfeatures may be implemented using hardware or a combination of hardwareand software. For example, a system like the ones described herein mayinclude various controllers and/or processing devices located at variouspoints. A central computer may coordinate operation among the variouscontrollers or processing devices. The central computer, controllers,and processing devices may execute various software routines to effectcontrol and coordination of testing and calibration.

System operation can be controlled, at least in part, using one or morecomputer program products, e.g., one or more computer program tangiblyembodied in one or more non-transitory machine-readable media, forexecution by, or to control the operation of, one or more dataprocessing apparatus, e.g., a programmable processor, a computer,multiple computers, and/or programmable logic components.

A computer program can be written in any form of programming language,including compiled or interpreted languages, and it can be deployed inany form, including as a stand-alone program or as a module, component,subroutine, or other unit suitable for use in a computing environment. Acomputer program can be deployed to be executed on one computer or onmultiple computers at one site or distributed across multiple sites andinterconnected by a network.

Actions associated with implementing all or part of the operations ofthe particle therapy system described herein can be performed by one ormore programmable processors executing one or more computer programs toperform the functions described herein. All or part of the operationscan be implemented using special purpose logic circuitry, e.g., an FPGA(field programmable gate array) and/or an ASIC (application-specificintegrated circuit).

Processors suitable for the execution of a computer program include, byway of example, both general and special purpose microprocessors, andany one or more processors of any kind of digital computer. Generally, aprocessor will receive instructions and data from a read-only storagearea or a random access storage area or both. Elements of a computer(including a server) include one or more processors for executinginstructions and one or more storage area devices for storinginstructions and data. Generally, a computer will also include, or beoperatively coupled to receive data from, or transfer data to, or both,one or more machine-readable storage media, such as mass PCBs forstoring data, e.g., magnetic, magneto-optical disks, or optical disks.Non-transitory machine-readable storage media suitable for embodyingcomputer program instructions and data include all forms of non-volatilestorage area, including by way of example, semiconductor storage areadevices, e.g., EPROM, EEPROM, and flash storage area devices; magneticdisks, e.g., internal hard disks or removable disks; magneto-opticaldisks; and CD-ROM and DVD-ROM disks.

Any “electrical connection” as used herein may imply a direct physicalconnection or a connection that includes intervening components but thatnevertheless allows electrical signals to flow between connectedcomponents. Any “connection” involving electrical circuitry mentionedherein, unless stated otherwise, is an electrical connection and notnecessarily a direct physical connection regardless of whether the word“electrical” is used to modify “connection”.

Any two more of the foregoing implementations may be used in anappropriate combination in an appropriate particle accelerator (e.g., asynchrocyclotron). Likewise, individual features of any two more of theforegoing implementations may be used in an appropriate combination.

Elements of different implementations described herein may be combinedto form other implementations not specifically set forth above. Elementsmay be left out of the processes, systems, apparatus, etc., describedherein without adversely affecting their operation. Various separateelements may be combined into one or more individual elements to performthe functions described herein.

The example implementations described herein are not limited to use witha particle therapy system or to use with the example particle therapysystems described herein. Rather, the example implementations can beused in any appropriate system that directs accelerated particles to anoutput.

Additional information concerning the design of an exampleimplementation of a particle accelerator that may be used in a system asdescribed herein can be found in U.S. Provisional Application No.60/760,788, entitled “High-Field Superconducting Synchrocyclotron” andfiled Jan. 20, 2006; U.S. patent application Ser. No. 11/463,402,entitled “Magnet Structure For Particle Acceleration” and filed Aug. 9,2006; and U.S. Provisional Application No. 60/850,565, entitled“Cryogenic Vacuum Break Pneumatic Thermal Coupler” and filed Oct. 10,2006, all of which are incorporated herein by reference.

The following applications are incorporated by reference into thesubject application: the U.S. Provisional Application entitled“CONTROLLING INTENSITY OF A PARTICLE BEAM” (Application No. 61/707,466),the U.S. Provisional Application entitled “ADJUSTING ENERGY OF APARTICLE BEAM” (Application No. 61/707,515), the U.S. ProvisionalApplication entitled “ADJUSTING COIL POSITION” (Application No.61/707,548), the U.S. Provisional Application entitled “FOCUSING APARTICLE BEAM USING MAGNETIC FIELD FLUTTER” (Application No.61/707,572), the U.S. Provisional Application entitled “MAGNETIC FIELDREGENERATOR” (Application No. 61/707,590), the U.S. ProvisionalApplication entitled “FOCUSING A PARTICLE BEAM” (Application No.61/707,704), the U.S. Provisional Application entitled “CONTROLLINGPARTICLE THERAPY (Application No. 61/707,624), and the U.S. ProvisionalApplication entitled “CONTROL SYSTEM FOR A PARTICLE ACCELERATOR”(Application No. 61/707,645).

The following are also incorporated by reference into the subjectapplication: U.S. Pat. No. 7,728,311 which issued on Jun. 1, 2010, U.S.patent application Ser. No. 11/948,359 which was filed on Nov. 30, 2007,U.S. patent application Ser. No. 12/275,103 which was filed on Nov. 20,2008, U.S. patent application Ser. No. 11/948,662 which was filed onNov. 30, 2007, U.S. Provisional Application No. 60/991,454 which wasfiled on Nov. 30, 2007, U.S. Pat. No. 8,003,964 which issued on Aug. 23,2011, U.S. Pat. No. 7,208,748 which issued on Apr. 24, 2007, U.S. Pat.No. 7,402,963 which issued on Jul. 22, 2008, U.S. patent applicationSer. No. 13/148,000 filed Feb. 9, 2010, U.S. patent application Ser. No.11/937,573 filed on Nov. 9, 2007, U.S. patent application Ser. No.11/187,633, titled “A Programmable Radio Frequency Waveform Generatorfor a Synchrocyclotron,” filed Jul. 21, 2005, U.S. ProvisionalApplication No. 60/590,089, filed on Jul. 21, 2004, U.S. patentapplication Ser. No. 10/949,734, titled “A Programmable ParticleScatterer for Radiation Therapy Beam Formation”, filed Sep. 24, 2004,and U.S. Provisional Application No. 60/590,088, filed Jul. 21, 2005.

Any features of the subject application may be combined with one or moreappropriate features of the following: the U.S. Provisional Applicationentitled “CONTROLLING INTENSITY OF A PARTICLE BEAM” (Application No.61/707,466), the U.S. Provisional Application entitled “ADJUSTING ENERGYOF A PARTICLE BEAM” (Application No. 61/707,515), the U.S. ProvisionalApplication entitled “ADJUSTING COIL POSITION” (Application No.61/707,548), the U.S. Provisional Application entitled “FOCUSING APARTICLE BEAM USING MAGNETIC FIELD FLUTTER” (Application No.61/707,572), the U.S. Provisional Application entitled “MAGNETIC FIELDREGENERATOR” (Application No. 61/707,590), the U.S. ProvisionalApplication entitled “FOCUSING A PARTICLE BEAM” (Application No.61/707,704), the U.S. Provisional Application entitled “CONTROLLINGPARTICLE THERAPY (Application No. 61/707,624), and the U.S. ProvisionalApplication entitled “CONTROL SYSTEM FOR A PARTICLE ACCELERATOR”(Application No. 61/707,645), U.S. Pat. No. 7,728,311 which issued onJun. 1, 2010, U.S. patent application Ser. No. 11/948,359 which wasfiled on Nov. 30, 2007, U.S. patent application Ser. No. 12/275,103which was filed on Nov. 20, 2008, U.S. patent application Ser. No.11/948,662 which was filed on Nov. 30, 2007, U.S. ProvisionalApplication No. 60/991,454 which was filed on Nov. 30, 2007, U.S. patentapplication Ser. No. 13/907,601, which was filed on May 31, 2013, U.S.patent application Ser. No. 13/916,401, filed on Jun. 12, 2013, U.S.Pat. No. 8,003,964 which issued on Aug. 23, 2011, U.S. Pat. No.7,208,748 which issued on Apr. 24, 2007, U.S. Pat. No. 7,402,963 whichissued on Jul. 22, 2008, U.S. patent application Ser. No. 13/148,000filed Feb. 9, 2010, U.S. patent application Ser. No. 11/937,573 filed onNov. 9, 2007, U.S. patent application Ser. No. 11/187,633, titled “AProgrammable Radio Frequency Waveform Generator for a Synchrocyclotron,”filed Jul. 21, 2005, U.S. Provisional Application No. 60/590,089, filedon Jul. 21, 2004, U.S. patent application Ser. No. 10/949,734, titled “AProgrammable Particle Scatterer for Radiation Therapy Beam Formation”,filed Sep. 24, 2004, and U.S. Provisional Application No. 60/590,088,filed Jul. 21, 2005.

Other implementations not specifically described herein are also withinthe scope of the following claims.

What is claimed is:
 1. A particle therapy system comprising: a particleaccelerator to output a particle beam; a scanning system for theparticle accelerator to scan the particle beam across at least part ofan irradiation target in a patient, the scanning system being configuredto scan the particle beam in at least two dimensions across the at leastpart of the irradiation target; and a collimator comprising multipleelements that are controllable to move in the at least two dimensionsrelative to the particle beam during scanning to track motion of theparticle beam as the particle beam is scanned across the at least partof the irradiation target, the multiple elements comprising a materialthat inhibits transmission of the particle beam, each of the multipleelements comprising fingers that are extendible and retractable in oneof the two dimensions to define an edge of the collimator that ismovable between a first part of the particle beam and the patient toprevent the first part of the particle beam from reaching the patientwhile allowing a second part of the particle beam to reach the at leastpart of the irradiation target.
 2. The particle therapy system of claim1, wherein each of the multiple elements is rotatable.
 3. The particletherapy system of claim 1, wherein the fingers are adjustable to vary asize of the edge.
 4. The particle therapy system of claim 1, wherein thefingers are individually movable relative to the irradiation target. 5.The particle therapy system of claim 1, wherein the multiple elementscomprise a first element and a second element, the first element fordefining the edge, the edge being a first edge, and the second elementfor defining a second edge; and wherein the first edge and the secondedge are controllable to move relative to the irradiation target.
 6. Theparticle therapy system of claim 1, wherein the scanning systemcomprises at least one magnet to control movement of the particle beamto scan the particle beam, the at least one magnet for generating amagnetic field in response to applied current, the magnetic fieldaffecting the movement.
 7. The particle therapy system of claim 1,wherein the scanning system is configured to scan the particle beam morequickly in interior sections of the irradiation target than at aperimeter of the irradiation target.
 8. The particle therapy system ofclaim 1, wherein the particle beam is movable within an area of a plane;and wherein the scanning system comprises an energy degrader having anarea that is less than the area of the plane.
 9. The particle therapysystem of claim 8, wherein the energy degrader has an area that is lessthan half the area of the plane.
 10. The particle therapy system ofclaim 8, wherein the energy degrader has an area that is less than aquarter the area of the plane.
 11. The particle therapy system of claim8, wherein the energy degrader has an area that is less than an eighththe area of the plane.
 12. The particle therapy system of claim 8,wherein the energy degrader has an area that is less than ten times across-sectional area of the particle beam.
 13. The particle therapysystem of claim 1, wherein the scanning system is configured to scan theparticle beam from different incident angles; and wherein the multipleelements are controllable to move based on movement of the particle beamas the particle beam is scanned from different incident angles.
 14. Theparticle therapy system of claim 1, wherein the scanning systemcomprises: a magnet to affect a direction of the particle beam to scanthe particle beam across the at least part of an irradiation target; anda degrader to change an energy of the beam prior to application of theparticle beam to the irradiation target, the degrader being down-beam ofthe magnet relative to the particle accelerator; wherein the particleaccelerator is a variable-energy synchrocyclotron.
 15. The particletherapy system of claim 1, wherein the particle accelerator is asynchrocyclotron.
 16. A particle therapy system comprising: a particleaccelerator to output a particle beam to treat an irradiation target ina patient; a scanning system for the particle accelerator to scan theparticle beam across at least part of the irradiation target, thescanning system being configured to scan the particle beam in at leasttwo dimensions that are at an angle relative to a direction of theparticle beam; and a collimator comprising multiple elements that arecontrollable to move in the at least two dimensions relative to theparticle beam to track movement of the particle beam as the particlebeam is scanned across the at least part of the irradiation target, themultiple elements comprising a material that inhibits transmission ofthe particle beam, and each of the multiple elements comprising fingersthat are extendible and retractable in one of the two dimensions todefine an edge of the collimator that is movable between a first part ofthe particle beam and the patient to prevent the first part of theparticle beam from reaching the patient while allowing a second part ofthe particle beam to reach the at least part of the irradiation target;wherein the particle accelerator comprises: a voltage source to providea radio frequency (RF) voltage to a cavity to accelerate particles froma plasma column, the cavity having a magnetic field causing particlesaccelerated from the plasma column to move orbitally within the cavity;an extraction channel to receive the particles accelerated from theplasma column and to output the received particles from the cavity; anda regenerator to provide a magnetic field bump within the cavity tothereby change successive orbits of the particles accelerated from theplasma column so that, eventually, particles output to the extractionchannel; wherein the magnetic field is between 4 Tesla (T) and 20 T andthe magnetic field bump is at most 2 Tesla.
 17. The particle therapysystem of claim 16, wherein the multiple elements are rotatable.
 18. Theparticle therapy system of claim 16, wherein the fingers are adjustableto vary a size of the edge.
 19. The particle therapy system of claim 16,wherein the fingers are individually movable relative to the irradiationtarget.
 20. The particle therapy system of claim 16, wherein themultiple elements comprise a first element and a second element, thefirst element for defining the edge, the edge being a first edge, andthe second element for defining a second edge; and wherein the firstedge and the second edge are controllable to move relative to theirradiation target.
 21. The particle therapy system of claim 16, whereinthe scanning system comprises at least one magnet to control movement ofthe particle beam to scan the particle beam, the at least one magnet forgenerating a magnetic field in response to applied current, the magneticfield affecting the movement.
 22. The particle therapy system of claim16, wherein the scanning system is configured to scan the particle beammore quickly in interior sections of the irradiation target than at aperimeter of the irradiation target.
 23. The particle therapy system ofclaim 16, wherein the particle beam is movable within an area of aplane; and wherein the scanning system comprises an energy degraderhaving an area that is less than the area of the plane.
 24. The particletherapy system of claim 23, wherein the energy degrader has an area thatis less than half the area of the plane.
 25. The particle therapy systemof claim 23, wherein the energy degrader has an area that is less than aquarter the area of the plane.
 26. The particle therapy system of claim23, wherein the energy degrader has an area that is less than an eighththe area of the plane.
 27. The particle therapy system of claim 23,wherein the energy degrader has an area that is less than ten times across-sectional area of the particle beam.
 28. The particle therapysystem of claim 16, wherein the scanning system is configured to scanthe particle beam from different incident angles; and wherein themultiple elements are controllable to move based on movement of theparticle beam as the particle beam is scanned from different incidentangles.
 29. The particle therapy system of claim 16, wherein thescanning system comprises: a magnet to affect a direction of theparticle beam to scan the particle beam across the at least part of anirradiation target; and a degrader to change an energy of the particlebeam prior to application of the particle beam to the irradiationtarget, the degrader being down-beam of the magnet relative to theparticle accelerator; wherein the particle accelerator is avariable-energy synchrocyclotron.
 30. The particle therapy system ofclaim 16, wherein the particle accelerator is a synchrocyclotron.
 31. Aparticle therapy system comprising: a particle accelerator to output aparticle beam to treat an irradiation target in a patient; a scanningsystem to perform scanning of at least part of the irradiation targetwith the particle beam; a collimator comprised of multiple elements thatare controllable to move in at least two dimensions relative to theparticle beam during scanning to track motion of the particle beam asthe particle beam is scanned across the at least part of the irradiationtarget, the multiple elements comprising a material that inhibitstransmission of the particle beam, and each of the multiple elementscomprising fingers that are extendible and retractable in one of the twodimensions to define an edge of the collimator that is movable between afirst part of the particle beam and the patient to prevent the firstpart of the particle beam from reaching the patient while allowing asecond part of the particle beam to reach the at least part ofirradiation target; and a gantry on which the particle accelerator ismounted, the gantry being configured to move the particle acceleratorrelative to the irradiation target.
 32. The particle therapy system ofclaim 31, wherein the multiple elements comprise a first element and asecond element, the first element for defining the edge, the edge beinga first edge, and the second element for defining a second edge; andwherein the first edge and the second edge are controllable to moverelative to the irradiation target.
 33. The particle therapy system ofclaim 31, wherein the multiple elements are rotatable.
 34. The particletherapy system of claim 31, wherein the scanning system is configured toscan the particle beam more quickly in interior sections of theirradiation target than at a perimeter of the irradiation target. 35.The particle therapy system of claim 31, wherein the scanning system isconfigured to scan the particle beam from different incident angles; andwherein the multiple elements are controllable to move based on movementof the particle beam as the particle beam is scanned from differentincident angles.
 36. The particle therapy system of claim 31, whereinthe particle accelerator is a synchrocyclotron.
 37. A particle therapysystem comprising: a particle accelerator to output a particle beam; ascanning system for the particle accelerator, the scanning system beingconfigured to move the particle beam across an irradiation field, theirradiation field comprising a maximum extent that the particle beam ismovable in at least two dimensions; and a collimator that is down-beamof the scanning system, the collimator comprising multiple elements, atleast one of the multiple elements comprising fingers that areextendible and retractable to define an edge of the collimator to blockat least part of the particle beam, the multiple elements beingcontrollable to move in the two dimensions relative to the particle beamwithin the irradiation field to track movement of the particle beam, thefingers of the at least one of the multiple elements being configurableduring movement of the particle beam to define the edge based on aposition of the particle beam relative to a target of the particle beam,wherein, for all configurations of the fingers, the edge extends acrossless than an extent of the irradiation field.
 38. The particle therapysystem of claim 37, wherein the multiple elements comprise a firstelement and a second element, the first element for defining the edge,the edge being a first edge, and the second element for defining asecond edge; and wherein the first edge and the second edge arecontrollable to move relative to the target.
 39. The particle therapysystem of claim 37, wherein the multiple elements are rotatable.
 40. Theparticle therapy system of claim 37, wherein the scanning system isconfigured to scan the particle beam more quickly in interior sectionsof the target than at a perimeter of the target.
 41. The particletherapy system of claim 37, wherein the scanning system is configured toscan the particle beam from different incident angles; and wherein themultiple elements are controllable to move based on movement of theparticle beam as the particle beam is scanned from different incidentangles.
 42. The particle therapy system of claim 37, wherein theparticle accelerator is a synchrocyclotron.